diff --git a/DECISIONS.md b/DECISIONS.md
index c7ac03d..96e8097 100644
--- a/DECISIONS.md
+++ b/DECISIONS.md
@@ -1051,3 +1051,11 @@ Implementation decisions not spelled out in `memory-bank/implementation-plan.md`
 - **Settings is a route (`/settings`) inside the normal layout**, reached only from the header gear, so the seven-tab navigation is unchanged and the back button works.
 - **Reduced motion is a three-way choice (Device / On / Off)**: "Device" stores no override, so the default keeps following the OS (decision 0.5.76).
 - **Items appear with the step that makes them work** (rename and new company, backup, version, developer tools), so no placeholder controls ship.
+
+## Step 10K.3
+
+- **The default "device" clock changes how the game clock looks** on 12-hour devices ("2145-07-11 7:18 PM"); before, it was always 24-hour. That is decision 0.5.76's default; players who prefer 24-hour pick it in Settings.
+- **Countdowns default to real time everywhere, Priority windows included.** CR-007's chip showed game hours and switched to real time on tap; it now shows the chosen countdown format, with both in its tooltip, so one setting governs every span.
+- **Game-time spans read "4.3 game h"** so they can't be mistaken for real hours next to a real countdown.
+- **Reduced motion has two sources**: the OS media query (unless the player turned motion back on) and the player's override. The map keeps moving ships but stills its background.
+- **Pure helpers read preferences directly** (`displayPreferences()`) where they format strings outside React (the dispatch sheet's problem lines); those re-render every second with the clock anyway.
diff --git a/apps/web/src/App.tsx b/apps/web/src/App.tsx
index 639de91..3bcf6be 100644
--- a/apps/web/src/App.tsx
+++ b/apps/web/src/App.tsx
@@ -15,6 +15,7 @@ import { Locations } from "./screens/Locations";
 import { Market } from "./screens/Market";
 import { Pilots } from "./screens/Pilots";
 import { Settings } from "./screens/Settings";
+import { useMotionPreference } from "./state/preferences";
 import { StartScreen } from "./screens/StartScreen";
 import { usePlayerState, useRefetchOnArrival } from "./state/player";
 import { Button } from "./ui";
@@ -50,6 +51,7 @@ function useServerClock() {
 /** The whole client. Router, API and query providers come from the caller. */
 export function App() {
   useServerClock();
+  useMotionPreference();
   const state = usePlayerState();
   useRefetchOnArrival(state.data ?? null, state.refetch);
   const retry = () => void state.refetch();
diff --git a/apps/web/src/clock/GameClock.tsx b/apps/web/src/clock/GameClock.tsx
index 4624e4b..aa7d0c5 100644
--- a/apps/web/src/clock/GameClock.tsx
+++ b/apps/web/src/clock/GameClock.tsx
@@ -1,14 +1,14 @@
 import { content } from "@deadhead/content";
 import { realToGame } from "@deadhead/sim";
+import { usePreferences } from "../state/preferences";
 import { useClock } from "./clock";
+import { formatGameTime } from "./timeFormat";
 
-/** "2100-03-14 08:00": the in-game date and hour, in UTC. */
-export function formatGameTime(gameTime: number): string {
-  return new Date(gameTime).toISOString().slice(0, 16).replace("T", " ");
-}
+export { formatGameTime };
 
-/** The ticking in-game clock shown in the header. */
+/** The ticking in-game clock shown in the header, in the player's clock format. */
 export function GameClock() {
   const now = useClock((state) => state.now);
-  return <time>{formatGameTime(realToGame(now, content.config))}</time>;
+  const clock = usePreferences((p) => p.clock);
+  return <time>{formatGameTime(realToGame(now, content.config), clock)}</time>;
 }
diff --git a/apps/web/src/clock/timeFormat.ts b/apps/web/src/clock/timeFormat.ts
new file mode 100644
index 0000000..f4c104b
--- /dev/null
+++ b/apps/web/src/clock/timeFormat.ts
@@ -0,0 +1,68 @@
+import { content } from "@deadhead/content";
+import { MS_PER_HOUR } from "@deadhead/sim";
+import { formatDuration } from "../format";
+import { usePreferences, type ClockFormat, type CountdownFormat } from "../state/preferences";
+
+/**
+ * The one place times and spans are formatted for display (CR-011): clock
+ * times follow the clock preference, spans follow the countdown preference.
+ */
+
+function hour12For(clock: ClockFormat): boolean | undefined {
+  return clock === "locale" ? undefined : clock === "12h";
+}
+
+/** A real time of day on this device, e.g. "14:05" or "2:05 PM". */
+export function formatTimeOfDay(time: number, clock: ClockFormat): string {
+  return new Date(time).toLocaleTimeString([], {
+    hour: "2-digit",
+    minute: "2-digit",
+    hour12: hour12For(clock),
+  });
+}
+
+/** The in-game date and time (UTC), e.g. "2100-03-14 08:00" or "2100-03-14 8:00 AM". */
+export function formatGameTime(gameTime: number, clock: ClockFormat = "24h"): string {
+  const date = new Date(gameTime).toISOString().slice(0, 10);
+  if (clock === "24h") return `${date} ${new Date(gameTime).toISOString().slice(11, 16)}`;
+  const time = new Date(gameTime).toLocaleTimeString([], {
+    hour: "numeric",
+    minute: "2-digit",
+    hour12: hour12For(clock),
+    timeZone: "UTC",
+  });
+  return `${date} ${time}`;
+}
+
+/** A span of game hours, e.g. "4.3 game h" or "62 game h". */
+export function formatGameSpan(gameHours: number): string {
+  const rounded = gameHours < 10 ? gameHours.toFixed(1) : String(Math.round(gameHours));
+  return `${rounded} game h`;
+}
+
+/**
+ * A span of real milliseconds as the player wants countdowns: real time
+ * ("4m 16s"), game time ("4.3 game h") or both ("4m 16s · 4.3 game h").
+ * `real` formats the real part (e.g. mm:ss for the board refresh).
+ */
+export function formatSpan(
+  ms: number,
+  mode: CountdownFormat,
+  real: (ms: number) => string = formatDuration,
+): string {
+  const game = formatGameSpan((Math.max(0, ms) * content.config.timeCompression) / MS_PER_HOUR);
+  if (mode === "game") return game;
+  if (mode === "both") return `${real(ms)} · ${game}`;
+  return real(ms);
+}
+
+/** A span given in game hours (e.g. a Priority window), in the countdown mode. */
+export function formatGameHoursSpan(gameHours: number, mode: CountdownFormat): string {
+  return formatSpan((gameHours * MS_PER_HOUR) / content.config.timeCompression, mode);
+}
+
+/** The current preferences, for formatting outside React components. */
+export function displayPreferences(): { clock: ClockFormat; countdown: CountdownFormat } {
+  const { clock, countdown } = usePreferences.getState();
+  return { clock, countdown };
+}
diff --git a/apps/web/src/components/Countdown.tsx b/apps/web/src/components/Countdown.tsx
index 9f99d83..21e28ff 100644
--- a/apps/web/src/components/Countdown.tsx
+++ b/apps/web/src/components/Countdown.tsx
@@ -1,7 +1,13 @@
 import { useClock } from "../clock/clock";
+import { formatSpan } from "../clock/timeFormat";
 import { formatDuration } from "../format";
+import { usePreferences } from "../state/preferences";
 
-/** Live time remaining until `to` (server clock); shows `done` once it has passed. */
+/**
+ * Live time remaining until `to` (server clock), in the player's countdown
+ * format (real, game or both; CR-011); shows `done` once it has passed.
+ * `format` styles the real-time part (e.g. mm:ss).
+ */
 export function Countdown({
   to,
   done = "Arriving…",
@@ -12,6 +18,11 @@ export function Countdown({
   format?: (ms: number) => string;
 }) {
   const now = useClock((s) => s.now);
+  const mode = usePreferences((p) => p.countdown);
   const remaining = to - now;
-  return <span className="tabular-nums">{remaining > 0 ? format(remaining) : done}</span>;
+  return (
+    <span className="tabular-nums">
+      {remaining > 0 ? formatSpan(remaining, mode, format) : done}
+    </span>
+  );
 }
diff --git a/apps/web/src/components/Goods.tsx b/apps/web/src/components/Goods.tsx
index cfbe224..681cf36 100644
--- a/apps/web/src/components/Goods.tsx
+++ b/apps/web/src/components/Goods.tsx
@@ -1,8 +1,9 @@
 import { content } from "@deadhead/content";
 import type { Contract, PlayerState } from "@deadhead/schema";
 import { contractTripGameHours, MS_PER_HOUR } from "@deadhead/sim";
+import { formatGameHoursSpan } from "../clock/timeFormat";
+import { usePreferences } from "../state/preferences";
 import { shipStatsOf } from "../game";
-import { useState } from "react";
 import { cargoName, formatDuration } from "../format";
 import { Pill, type Tone } from "../ui";
 
@@ -41,25 +42,20 @@ export function ClassChip({ contract }: { contract: Pick<Contract, "cargoTypeId"
 }
 
 /**
- * "PRIORITY · within 5h" (game hours). Tap to switch to real time; hovering
- * shows both.
+ * "PRIORITY · within 5m 00s": the delivery window, in the player's countdown
+ * format (CR-011); hovering shows game and real time.
  */
 export function PriorityChip({ windowHours }: { windowHours: number }) {
-  const [real, setReal] = useState(false);
+  const mode = usePreferences((p) => p.countdown);
   return (
-    <button
-      type="button"
-      onClick={() => setReal(!real)}
+    <span
       title={`Within ${formatWindow(windowHours)} game time, about ${realTimeOf(windowHours)} real time`}
-      className="rounded-full"
     >
       <Pill tone="amber" icon="bolt">
         Priority · within{" "}
-        <span className="normal-case">
-          {real ? realTimeOf(windowHours) : formatWindow(windowHours)}
-        </span>
+        <span className="normal-case">{formatGameHoursSpan(windowHours, mode)}</span>
       </Pill>
-    </button>
+    </span>
   );
 }
 
diff --git a/apps/web/src/index.css b/apps/web/src/index.css
index ffc9b44..b1d4e79 100644
--- a/apps/web/src/index.css
+++ b/apps/web/src/index.css
@@ -95,13 +95,24 @@
   }
 }
 
-/* Motion is decoration only: switch it off when asked. */
+/*
+ * Motion is decoration only: switch it off when asked. The app sets
+ * data-reduced-motion on <html> from the player's setting (CR-011); without
+ * an override it follows the device.
+ */
 @media (prefers-reduced-motion: reduce) {
-  *,
-  *::before,
-  *::after {
+  :root:not([data-reduced-motion="false"]) *,
+  :root:not([data-reduced-motion="false"]) *::before,
+  :root:not([data-reduced-motion="false"]) *::after {
     animation-duration: 0.01ms !important;
     animation-iteration-count: 1 !important;
     transition-duration: 0.01ms !important;
   }
 }
+:root[data-reduced-motion="true"] *,
+:root[data-reduced-motion="true"] *::before,
+:root[data-reduced-motion="true"] *::after {
+  animation-duration: 0.01ms !important;
+  animation-iteration-count: 1 !important;
+  transition-duration: 0.01ms !important;
+}
diff --git a/apps/web/src/map/layout.ts b/apps/web/src/map/layout.ts
index a153574..8a833c4 100644
--- a/apps/web/src/map/layout.ts
+++ b/apps/web/src/map/layout.ts
@@ -310,3 +310,11 @@ export function decorate(
   }
   return result;
 }
+
+/**
+ * The map style with motion settings applied (CR-011): reduced motion keeps the
+ * background still (no parallax, no zoom follow). Ships still move.
+ */
+export function mapMotionStyle(reducedMotion: boolean, style: MapStyle = mapStyle): MapStyle {
+  return reducedMotion ? { ...style, parallax: 0, backgroundZoomFollow: 0 } : style;
+}
diff --git a/apps/web/src/map/renderer.ts b/apps/web/src/map/renderer.ts
index 613c177..09ca9a0 100644
--- a/apps/web/src/map/renderer.ts
+++ b/apps/web/src/map/renderer.ts
@@ -2,7 +2,8 @@ import { ColorMatrixFilter, Container, Graphics, Sprite, Text, type Texture } fr
 import type { ArtTextures } from "./art/load";
 import { sceneVisuals, type Visual } from "./art/visuals";
 import { toScreen, type Camera, type Viewport } from "./camera";
-import { backgroundRect, decorate, layoutScene, polar } from "./layout";
+import { reducedMotionOn, usePreferences } from "../state/preferences";
+import { backgroundRect, decorate, layoutScene, mapMotionStyle, polar } from "./layout";
 import type { MapSelection } from "./hitTest";
 import { locationOverlays } from "./overlays";
 import type { MapPoint } from "./projection";
@@ -136,7 +137,8 @@ export class MapRenderer {
     for (const sprite of this.sprites.values()) sprite.visible = false;
 
     if (this.background) {
-      const r = backgroundRect(view, camera, this.background.texture);
+      const style = mapMotionStyle(reducedMotionOn(usePreferences.getState()));
+      const r = backgroundRect(view, camera, this.background.texture, style);
       this.background.position.set(r.x, r.y);
       this.background.setSize(r.width, r.height);
     }
diff --git a/apps/web/src/screens/DispatchSheet.tsx b/apps/web/src/screens/DispatchSheet.tsx
index b6dd34a..0dbfb49 100644
--- a/apps/web/src/screens/DispatchSheet.tsx
+++ b/apps/web/src/screens/DispatchSheet.tsx
@@ -31,7 +31,14 @@ import { location, tripRealMs, shipStatsOf, simShip } from "../game";
 import { errorMessage, useGameAction, useLoadedPlayer } from "../state/actions";
 import { RouteStrip } from "../components/RouteStrip";
 import { Art, Button, Sheet } from "../ui";
-import { formatWindow, goodName, PriorityChip } from "../components/Goods";
+import { goodName, PriorityChip } from "../components/Goods";
+import {
+  displayPreferences,
+  formatGameHoursSpan,
+  formatSpan,
+  formatTimeOfDay,
+} from "../clock/timeFormat";
+import { usePreferences } from "../state/preferences";
 
 /** Short player-facing reasons a ship+pilot cannot take a contract. */
 export const INELIGIBLE_REASONS: Record<DispatchFailure, string> = {
@@ -68,7 +75,9 @@ export function explainProblems(
   const problems: string[] = [];
   // Resting blocks flying (CR-004): first, with the time left.
   if (pilot.resting && pilot.restEndsAt !== null) {
-    problems.push(`Resting — ${formatClock(pilot.restEndsAt - now)}`);
+    problems.push(
+      `Resting — ${formatSpan(pilot.restEndsAt - now, displayPreferences().countdown, formatClock)}`,
+    );
   }
   if (pilot.status === "in-flight") problems.push(INELIGIBLE_REASONS["pilot-not-idle"]);
   if (contract.massTonnes > model.cargoCapacityTonnes) {
@@ -92,7 +101,9 @@ export function explainProblems(
   if (window !== null) {
     const trip = contractTripGameHours(model, contract, now, content);
     if (trip > window) {
-      problems.push(`Too slow — ${formatWindow(trip)} vs ${formatWindow(window)} window`);
+      problems.push(
+        `Too slow — ${formatGameHoursSpan(trip, displayPreferences().countdown)} vs ${formatGameHoursSpan(window, displayPreferences().countdown)} window`,
+      );
     }
   }
   if (contract.requiredSkill) {
@@ -116,7 +127,7 @@ export function explainProblems(
 
 /** Real-world arrival time on the device, e.g. "14:05". */
 export function formatLocalTime(time: number): string {
-  return new Date(time).toLocaleTimeString([], { hour: "2-digit", minute: "2-digit" });
+  return formatTimeOfDay(time, displayPreferences().clock);
 }
 
 export interface PairOption {
@@ -201,7 +212,9 @@ export function pairOptions(state: PlayerState, contract: Contract, now: number)
           const all = explainProblems(state, contract, model, pilot, fuelCost, gameNow, now);
           // In the shop (CR-009): first, with the time left.
           if (isInShop(ship, now))
-            all.unshift(`In the shop — ${formatClock(ship.inShopUntil! - now)}`);
+            all.unshift(
+              `In the shop — ${formatSpan(ship.inShopUntil! - now, displayPreferences().countdown, formatClock)}`,
+            );
           problems = all.length > 0 ? all : [INELIGIBLE_REASONS[check.reason]];
         }
       }
@@ -233,6 +246,7 @@ export function pairOptions(state: PlayerState, contract: Contract, now: number)
 /** Choose a ship and pilot for a contract, see the numbers, and confirm (Step 9.5). */
 export function DispatchSheet({ contract, onClose }: { contract: Contract; onClose: () => void }) {
   const state = useLoadedPlayer();
+  const prefsCountdown = usePreferences((p) => p.countdown);
   const now = useClock((s) => s.now);
   const dispatch = useGameAction("createDispatch");
   const options = pairOptions(state, contract, now);
@@ -339,7 +353,10 @@ export function DispatchSheet({ contract, onClose }: { contract: Contract; onClo
                       <Cell label="Net profit" value={formatCredits(option.netProfit)} good />
                       <Cell
                         label="ETA (game)"
-                        value={formatGameTime(realToGame(option.arrivalAt, content.config))}
+                        value={formatGameTime(
+                          realToGame(option.arrivalAt, content.config),
+                          displayPreferences().clock,
+                        )}
                       />
                       <Cell label="ETA (real)" value={formatLocalTime(option.arrivalAt)} />
                       {option.duty && (
@@ -352,9 +369,14 @@ export function DispatchSheet({ contract, onClose }: { contract: Contract; onClo
                   )}
                   {!blocked && option.priority && (
                     <p aria-label="Priority margin" className="mt-2 text-amber-200">
-                      Priority: {formatWindow(option.priority.tripHours)} trip,{" "}
-                      {formatWindow(option.priority.windowHours - option.priority.tripHours)} to
-                      spare in the {formatWindow(option.priority.windowHours)} window
+                      Priority: {formatGameHoursSpan(option.priority.tripHours, prefsCountdown)}{" "}
+                      trip,{" "}
+                      {formatGameHoursSpan(
+                        option.priority.windowHours - option.priority.tripHours,
+                        prefsCountdown,
+                      )}{" "}
+                      to spare in the{" "}
+                      {formatGameHoursSpan(option.priority.windowHours, prefsCountdown)} window
                     </p>
                   )}
                   {!blocked && option.duty?.willRest && (
diff --git a/apps/web/src/screens/HQ.tsx b/apps/web/src/screens/HQ.tsx
index 1442f26..2142493 100644
--- a/apps/web/src/screens/HQ.tsx
+++ b/apps/web/src/screens/HQ.tsx
@@ -10,6 +10,7 @@ import { LoanCard } from "../components/LoanCard";
 import { RouteStrip } from "../components/RouteStrip";
 import { formatCredits, locationName } from "../format";
 import { useLoadedPlayer } from "../state/actions";
+import { usePreferences } from "../state/preferences";
 import { buttonClass, Eyebrow, Icon, Panel, Screen, ScreenHeader, StatTile } from "../ui";
 
 /** What the player needs to do next to reach the deal (decision 0.5.30). */
@@ -27,6 +28,7 @@ export function tutorialHint(tutorial: TutorialState, runsBeforeDeal: number): s
 export function HQ() {
   const state = useLoadedPlayer();
   const now = useClock((s) => s.now);
+  const clockFormat = usePreferences((p) => p.clock);
   const idle = state.ships.filter((s) => s.status === "idle").length;
   const flying = state.ships.filter((s) => s.status === "in-flight").length;
   const runsBeforeDeal = content.config.tutorialRunsBeforeDeal;
@@ -56,7 +58,7 @@ export function HQ() {
         />
         <StatTile
           label="Game date"
-          value={formatGameTime(realToGame(now, content.config))}
+          value={formatGameTime(realToGame(now, content.config), clockFormat)}
           icon="clock"
         />
         <StatTile label="Ships idle" value={String(idle)} icon="fleet" tone="emerald" />
diff --git a/apps/web/src/screens/MapScreen.tsx b/apps/web/src/screens/MapScreen.tsx
index a63673a..7ce3209 100644
--- a/apps/web/src/screens/MapScreen.tsx
+++ b/apps/web/src/screens/MapScreen.tsx
@@ -12,6 +12,7 @@ import type { MapSelection } from "../map/hitTest";
 import { MapCanvas } from "../map/MapCanvas";
 import { modelsReachingFromEarth, upgradedShipsReachingFromEarth } from "../map/reach";
 import { useLoadedPlayer } from "../state/actions";
+import { usePreferences } from "../state/preferences";
 import { Art, buttonClass, Icon } from "../ui";
 
 const TYPE_LABELS: Record<Location["type"], string> = {
@@ -157,6 +158,7 @@ function LocationPanel({ locationId, onClose }: { locationId: string; onClose: (
 /** A tapped ship in flight: its route, pilot and ETA. */
 function FlightPanel({ dispatchId, onClose }: { dispatchId: string; onClose: () => void }) {
   const state = useLoadedPlayer();
+  const clockFormat = usePreferences((p) => p.clock);
   const dispatch = state.activeDispatches.find((d) => d.id === dispatchId);
   if (!dispatch) return null;
   const shipName = dispatch.tutorial
@@ -183,7 +185,7 @@ function FlightPanel({ dispatchId, onClose }: { dispatchId: string; onClose: ()
         <span className="font-display text-cyan-200">
           <Countdown to={dispatch.arrivalAt} />
         </span>{" "}
-        ({formatGameTime(realToGame(dispatch.arrivalAt, content.config))})
+        ({formatGameTime(realToGame(dispatch.arrivalAt, content.config), clockFormat)})
       </p>
     </Panel>
   );
diff --git a/apps/web/src/state/preferences.ts b/apps/web/src/state/preferences.ts
index 1dcd380..24aa612 100644
--- a/apps/web/src/state/preferences.ts
+++ b/apps/web/src/state/preferences.ts
@@ -1,3 +1,4 @@
+import { useEffect } from "react";
 import { create, type StoreApi, type UseBoundStore } from "zustand";
 import type { Camera } from "../map/camera";
 
@@ -132,3 +133,16 @@ export const usePreferences = createPreferencesStore();
 export function reducedMotionOn(prefs: Pick<Preferences, "reducedMotion">): boolean {
   return prefs.reducedMotion ?? deviceReducesMotion();
 }
+
+/**
+ * Mirrors the reduced-motion override onto `<html data-reduced-motion>`, which
+ * the stylesheet uses; no attribute means "follow the device".
+ */
+export function useMotionPreference(): void {
+  const override = usePreferences((p) => p.reducedMotion);
+  useEffect(() => {
+    const root = document.documentElement;
+    if (override === null) delete root.dataset.reducedMotion;
+    else root.dataset.reducedMotion = String(override);
+  }, [override]);
+}
diff --git a/apps/web/test/clock.test.tsx b/apps/web/test/clock.test.tsx
index 7aa7f4d..4bf1464 100644
--- a/apps/web/test/clock.test.tsx
+++ b/apps/web/test/clock.test.tsx
@@ -52,7 +52,8 @@ describe("server-synced clock", () => {
     await syncClock(serverAhead(0));
     const stop = startClockTicker();
     render(<GameClock />);
-    const at = (real: number) => formatGameTime(realToGame(real, content.config));
+    // The default clock follows the device locale (CR-011).
+    const at = (real: number) => formatGameTime(realToGame(real, content.config), "locale");
     expect(screen.getByText(at(DEVICE_NOW))).toBeInTheDocument();
 
     // One real minute is one game hour.
diff --git a/apps/web/test/contract-card.test.tsx b/apps/web/test/contract-card.test.tsx
index ac1b5be..89b861d 100644
--- a/apps/web/test/contract-card.test.tsx
+++ b/apps/web/test/contract-card.test.tsx
@@ -1,6 +1,5 @@
 import type { Contract, Ship } from "@deadhead/schema";
 import { screen, within } from "@testing-library/react";
-import userEvent from "@testing-library/user-event";
 import { describe, expect, it } from "vitest";
 import { realTimeOf } from "../src/components/Goods";
 import { fakeApi, renderApp, samplePlayerState, shipExtras } from "./render";
@@ -78,9 +77,8 @@ describe("contract card (CR-007)", () => {
     const c = await card("3,210 cr");
     // A Priority good can have its own name.
     expect(within(c).getByRole("heading", { name: "Emergency Parts" })).toBeInTheDocument();
-    const chip = within(c).getByRole("button", { name: /Priority · within 5h/ });
-    await userEvent.click(chip);
-    expect(chip).toHaveTextContent(`Priority · within ${realTimeOf(5)}`);
+    // The window follows the countdown preference: real time by default (CR-011).
+    expect(c).toHaveTextContent(`Priority · within ${realTimeOf(5)}`);
     expect(c).not.toHaveTextContent("Too slow");
   });
 
diff --git a/apps/web/test/dispatch-priority.test.tsx b/apps/web/test/dispatch-priority.test.tsx
index 82c646a..d6ff24c 100644
--- a/apps/web/test/dispatch-priority.test.tsx
+++ b/apps/web/test/dispatch-priority.test.tsx
@@ -4,8 +4,8 @@ import { contractTripGameHours, priorityWindow } from "@deadhead/sim";
 import { screen, within } from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { formatGameHoursSpan } from "../src/clock/timeFormat";
 import { useClock } from "../src/clock/clock";
-import { formatWindow } from "../src/components/Goods";
 import { fakeApi, renderApp, samplePlayerState, shipExtras } from "./render";
 
 const NOW = Date.parse("2100-01-01T00:00:00Z");
@@ -102,7 +102,7 @@ describe("Priority in the dispatch sheet (CR-007)", () => {
     const fast = option(await openSheet(), "Quick Finch");
     expect(within(fast).getByRole("radio")).toBeEnabled();
     expect(within(fast).getByLabelText("Priority margin")).toHaveTextContent(
-      `Priority: ${formatWindow(trip("courier"))} trip, ${formatWindow(window - trip("courier"))} to spare in the ${formatWindow(window)} window`,
+      `Priority: ${formatGameHoursSpan(trip("courier"), "real")} trip, ${formatGameHoursSpan(window - trip("courier"), "real")} to spare in the ${formatGameHoursSpan(window, "real")} window`,
     );
   });
 
@@ -112,7 +112,7 @@ describe("Priority in the dispatch sheet (CR-007)", () => {
     const slow = option(await openSheet(), "Old Barge");
     expect(within(slow).getByRole("radio")).toBeDisabled();
     expect(within(slow).getByRole("list", { name: "Problems" })).toHaveTextContent(
-      `Too slow — ${formatWindow(trip("bulk-hauler"))} vs ${formatWindow(window)} window`,
+      `Too slow — ${formatGameHoursSpan(trip("bulk-hauler"), "real")} vs ${formatGameHoursSpan(window, "real")} window`,
     );
   });
 });
diff --git a/apps/web/test/dispatch-sheet.test.tsx b/apps/web/test/dispatch-sheet.test.tsx
index 36e927f..93abab7 100644
--- a/apps/web/test/dispatch-sheet.test.tsx
+++ b/apps/web/test/dispatch-sheet.test.tsx
@@ -134,7 +134,7 @@ describe("dispatch sheet", () => {
     expect(freighter).toHaveTextContent(`Fuel${formatCredits(fuel)}`);
     expect(freighter).toHaveTextContent(`Net profit${formatCredits(net)}`);
     expect(freighter).toHaveTextContent(
-      `ETA (game)${formatGameTime(realToGame(NOW + tripMs, content.config))}`,
+      `ETA (game)${formatGameTime(realToGame(NOW + tripMs, content.config), "locale")}`,
     );
     expect(freighter).toHaveTextContent(`ETA (real)${formatLocalTime(NOW + tripMs)}`);
   });
diff --git a/apps/web/test/display-options.test.tsx b/apps/web/test/display-options.test.tsx
new file mode 100644
index 0000000..607244b
--- /dev/null
+++ b/apps/web/test/display-options.test.tsx
@@ -0,0 +1,112 @@
+import { content } from "@deadhead/content";
+import type { Contract } from "@deadhead/schema";
+import { MS_PER_HOUR, realToGame } from "@deadhead/sim";
+import { act, screen } from "@testing-library/react";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { useClock } from "../src/clock/clock";
+import {
+  formatGameHoursSpan,
+  formatGameSpan,
+  formatGameTime,
+  formatSpan,
+  formatTimeOfDay,
+} from "../src/clock/timeFormat";
+import { formatClock } from "../src/format";
+import { mapMotionStyle } from "../src/map/layout";
+import { mapStyle } from "../src/map/style";
+import { DEFAULT_PREFERENCES, usePreferences } from "../src/state/preferences";
+import { fakeApi, renderApp, samplePlayerState } from "./render";
+
+const NOW = Date.parse("2100-01-01T00:00:00Z");
+/** 4m 16s of real time is 4.27 game hours at 60× compression. */
+const SPAN = 4 * 60_000 + 16_000;
+
+describe("time and span helpers (Step 10K.3)", () => {
+  it("formats game time in 24-hour and 12-hour clocks", () => {
+    const t = Date.parse("2100-03-14T13:05:00Z");
+    expect(formatGameTime(t, "24h")).toBe("2100-03-14 13:05");
+    expect(formatGameTime(t, "12h")).toMatch(/^2100-03-14 1:05\sPM$/);
+  });
+
+  it("formats a real time of day in each clock mode", () => {
+    const t = new Date(2100, 0, 1, 15, 7).getTime();
+    expect(formatTimeOfDay(t, "24h")).toBe("15:07");
+    expect(formatTimeOfDay(t, "12h")).toMatch(/^0?3:07\sPM$/);
+    expect(formatTimeOfDay(t, "locale")).toBe(
+      new Date(t).toLocaleTimeString([], { hour: "2-digit", minute: "2-digit" }),
+    );
+  });
+
+  it("formats spans as real time, game time or both", () => {
+    expect(formatSpan(SPAN, "real")).toBe("4m 16s");
+    expect(formatSpan(SPAN, "game")).toBe("4.3 game h");
+    expect(formatSpan(SPAN, "both")).toBe("4m 16s · 4.3 game h");
+    expect(formatSpan(SPAN, "both", formatClock)).toBe("04:16 · 4.3 game h");
+    expect(formatGameSpan(62.4)).toBe("62 game h");
+    expect(formatGameHoursSpan(5, "game")).toBe("5.0 game h");
+    expect(formatGameHoursSpan(5, "real")).toBe(
+      formatSpan((5 * MS_PER_HOUR) / content.config.timeCompression, "real"),
+    );
+  });
+
+  it("stills the map background with reduced motion", () => {
+    expect(mapMotionStyle(true).parallax).toBe(0);
+    expect(mapMotionStyle(true).backgroundZoomFollow).toBe(0);
+    expect(mapMotionStyle(false).parallax).toBe(mapStyle.parallax);
+  });
+});
+
+describe("display options in the app (Step 10K.3)", () => {
+  beforeEach(() => {
+    vi.useFakeTimers({ toFake: ["Date", "setInterval", "clearInterval"] });
+    vi.setSystemTime(NOW);
+    useClock.setState({ offsetMs: 0, synced: true, now: NOW });
+  });
+  afterEach(() => {
+    vi.useRealTimers();
+    act(() => usePreferences.getState().set(DEFAULT_PREFERENCES));
+  });
+
+  it("switches the HQ clock to 24-hour", async () => {
+    act(() => usePreferences.getState().set({ clock: "12h" }));
+    renderApp(fakeApi({ getPlayerState: () => samplePlayerState({ tutorial: null }) }), "/");
+    const game = realToGame(NOW, content.config);
+    expect(await screen.findByLabelText("Game clock")).toHaveTextContent(
+      formatGameTime(game, "12h"),
+    );
+    act(() => usePreferences.getState().set({ clock: "24h" }));
+    expect(screen.getByLabelText("Game clock")).toHaveTextContent(formatGameTime(game, "24h"));
+  });
+
+  it("shows contract expiry in both real and game time when asked", async () => {
+    const job: Contract = {
+      id: "c1",
+      originId: "earth",
+      destinationId: "moon",
+      cargoTypeId: "standard",
+      goodId: "consumer-goods",
+      shipper: "Pacific Orbital Logistics",
+      priority: false,
+      deliveryWindowGameHours: null,
+      tier: 0,
+      massTonnes: 10,
+      payout: 1234,
+      requiredSkill: null,
+      requiredLongHaulLevel: 0,
+      offeredAt: NOW,
+      expiresAt: NOW + SPAN,
+      firstContact: false,
+    };
+    renderApp(
+      fakeApi({
+        getPlayerState: () => samplePlayerState({ tutorial: null }),
+        getContractBoard: () => ({ contracts: [job], periodEndsAt: NOW + 600_000 }),
+      }),
+      "/contracts?location=earth",
+    );
+    const card = (await screen.findByText("1,234 cr")).closest("li")!;
+    expect(card).toHaveTextContent("expires in 4m 16s");
+    act(() => usePreferences.getState().set({ countdown: "both" }));
+    expect(card).toHaveTextContent("expires in 4m 16s · 4.3 game h");
+  });
+});
diff --git a/apps/web/test/layout.test.tsx b/apps/web/test/layout.test.tsx
index 4eda009..4560150 100644
--- a/apps/web/test/layout.test.tsx
+++ b/apps/web/test/layout.test.tsx
@@ -16,7 +16,8 @@ describe("app layout", () => {
     expect(await screen.findByRole("banner")).toBeInTheDocument();
     expect(screen.getByLabelText("Credits")).toHaveTextContent("1,234 cr");
     expect(screen.getByLabelText("Game clock")).toHaveTextContent(
-      /^\d{4}-\d{2}-\d{2} \d{2}:\d{2}$/,
+      // Device-locale clock by default (CR-011): 24-hour or 12-hour.
+      /^\d{4}-\d{2}-\d{2} \d{1,2}:\d{2}( [AP]M)?$/,
     );
     const nav = screen.getByRole("navigation", { name: "Main" });
     expect(within(nav).getAllByRole("link")).toHaveLength(SCREENS.length);
diff --git a/memory-bank/progress.md b/memory-bank/progress.md
index b1490de..35efb6d 100644
--- a/memory-bank/progress.md
+++ b/memory-bank/progress.md
@@ -254,7 +254,7 @@ Spec: `memory-bank/change-requests/CR-011-settings-backup.md` (received as "CR-0
 
 - [x] **Step 10K.1 — Client: device preferences store.** `state/preferences.ts`: `usePreferences` (Zustand) with clock (`locale`/`12h`/`24h`), countdown (`real`/`game`/`both`), reduced-motion override (null = follow the device), dismissed tips and saved map camera; `set`, `dismissTip`, `showTipsAgain`. Saved under `deadhead:preferences:v1`; loading validates each field and falls back to defaults; every read and write is wrapped. `reducedMotionOn(prefs)`. Test: `preferences.test.ts` (defaults incl. mocked OS reduced motion, survives a reload, broken data ignored, throwing storage works in memory).
 - [x] **Step 10K.2 — Client: settings screen and entry point.** A gear link (`aria-label="Settings"`, new `gear` icon) at the right of the header opens `/settings` (a route inside the layout, not a nav tab). `screens/Settings.tsx`: sections Company (name), Display (Clock: Device/12-hour/24-hour; Countdowns: Real time/Game time/Both; Reduced motion: Device/On/Off, saved to device preferences), Help (Reset map view, Show tips again), About (game name) and Developer, which renders only when `import.meta.env.PROD` is false. Remaining items arrive with their steps. Test: `settings.test.tsx`.
-- [ ] Step 10K.3 — Client: display options applied everywhere
+- [x] **Step 10K.3 — Client: display options applied everywhere.** `clock/timeFormat.ts`: `formatTimeOfDay` and `formatGameTime` follow the clock preference (header and HQ game clock, dispatch ETAs, map flight panel, "resting until"); `formatSpan` / `formatGameHoursSpan` follow the countdown preference ("4m 16s", "4.3 game h" or both) and drive `Countdown` (arrivals, rest, shop, board refresh, contract expiry) and the Priority chip, trip and too-slow texts. Reduced motion sets `<html data-reduced-motion>`, which the stylesheet uses alongside the OS query, and `mapMotionStyle` zeroes the map's parallax and zoom follow. The Priority chip no longer toggles on tap (it follows the preference; its tooltip shows both). Test: `display-options.test.tsx`; clock, layout, dispatch and contract-card tests updated for the new defaults.
 - [ ] Step 10K.4 — Client: reset map view and show tips again
 - [ ] Step 10K.5 — Server: rename company
 - [ ] Step 10K.6 — Server: start a new company