diff --git a/apps/mobile/src/features/threads/ThreadFeed.tsx b/apps/mobile/src/features/threads/ThreadFeed.tsx
index 6419c7dc7778..ba0445c6a4b2 100644
--- a/apps/mobile/src/features/threads/ThreadFeed.tsx
+++ b/apps/mobile/src/features/threads/ThreadFeed.tsx
@@ -288,7 +288,7 @@ import {
 import { ZoomableImagePressable } from "./ZoomableImagePressable";
 import { openSettings } from "../settings/settings-navigation";
 import { useSelectWorkspaceDetail } from "../layout/workspace/useSelectWorkspaceDetail";
-import { formatMessageTimestamp } from "./messageTimestamp";
+import { useMessageTimeFormatter } from "./useMessageTimeFormatter";
 
 const WIDE_MARKDOWN_BLOCK_OPTIONS = {
   // iOS blockquotes and selectable text measure separately; definite bubble width matches UIKit's drawing width.
@@ -1667,6 +1667,7 @@ function renderFeedEntry(
     | "threadId"
     | "workspaceRoot"
   > & {
+    readonly formatMessageTime: (input: string) => string;
     readonly copiedRowId: string | null;
     readonly expandedWorkRows: Record<string, boolean>;
     readonly workRowSizing: ReturnType<typeof deriveThreadWorkLogSizing>;
@@ -1912,7 +1913,7 @@ function renderFeedEntry(
     const presentation = resolveUserMessagePresentation(message);
     const renderedText = renderAssistantCitationsAsText(presentation.text);
     const styles = isUser ? markdownStyles.user : markdownStyles.assistant;
-    const timestampLabel = formatMessageTimestamp(isUser ? message.createdAt : message.updatedAt);
+    const timestampLabel = props.formatMessageTime(isUser ? message.createdAt : message.updatedAt);
     const attachments = message.attachments ?? [];
     const hasReviewCommentContext = presentation.text.includes("<review_comment");
     // Android does not reposition children after maxWidth clamps bubbles; definite width prevents wide-block overlap.
@@ -2740,6 +2741,7 @@ const THREAD_FEED_MAINTAIN_SCROLL_AT_END = {
 } as const;
 
 export const ThreadFeed = memo(function ThreadFeed(props: ThreadFeedProps) {
+  const formatMessageTime = useMessageTimeFormatter();
   const { listRef, onIsAtEndChange, onHeaderMaterialVisibilityChange } = props;
   const workflowOpening = useWorkflowOpening(props.detailRef);
   const guestShare = useThreadGuestShare(props.detailRef);
@@ -3341,6 +3343,7 @@ export const ThreadFeed = memo(function ThreadFeed(props: ThreadFeedProps) {
   const listAppearanceData = {
     disclosureLayout,
     reduceMotion,
+    formatMessageTime,
     worktreeSetup: props.worktreeSetup,
     setupWorkingStartedAt: props.setupWorkingStartedAt,
     dispatchingMessageId: props.dispatchingMessageId,
@@ -3751,6 +3754,7 @@ export const ThreadFeed = memo(function ThreadFeed(props: ThreadFeedProps) {
           ) : null}
           {renderFeedEntry(info, {
             userMessageGrouping: info.item.userMessageGrouping,
+            formatMessageTime,
             environmentId: props.environmentId,
             dispatchingMessageId: props.dispatchingMessageId,
             onEditPendingMessage: props.onEditPendingMessage,
diff --git a/apps/mobile/src/features/threads/messageTimestamp.test.ts b/apps/mobile/src/features/threads/messageTimestamp.test.ts
index 94f6010acd4a..fa1ab4be779b 100644
--- a/apps/mobile/src/features/threads/messageTimestamp.test.ts
+++ b/apps/mobile/src/features/threads/messageTimestamp.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, it } from "vite-plus/test";
 
-import { formatMessageTimestamp } from "./messageTimestamp";
+import { createMessageTimeFormatter, formatMessageTimestamp } from "./messageTimestamp";
 
 describe("formatMessageTimestamp", () => {
   const now = new Date(2026, 10, 8, 20, 0).getTime();
@@ -20,3 +20,15 @@ describe("formatMessageTimestamp", () => {
     );
   });
 });
+
+describe("createMessageTimeFormatter", () => {
+  const now = new Date(2026, 0, 1, 20, 0).getTime();
+
+  it("follows the system clock preference over the locale's hour cycle", () => {
+    const format24 = createMessageTimeFormatter(true, "en-US");
+    expect(format24(new Date(2026, 0, 1, 15, 7).toISOString(), now)).toBe("15:07");
+    expect(format24(new Date(2026, 0, 1, 0, 7).toISOString(), now)).toBe("00:07");
+    const format12 = createMessageTimeFormatter(false, "en-GB");
+    expect(format12(new Date(2026, 0, 1, 15, 7).toISOString(), now)).toMatch(/^3:07\spm$/i);
+  });
+});
diff --git a/apps/mobile/src/features/threads/messageTimestamp.ts b/apps/mobile/src/features/threads/messageTimestamp.ts
index 5624b71c0c91..cfae85e09266 100644
--- a/apps/mobile/src/features/threads/messageTimestamp.ts
+++ b/apps/mobile/src/features/threads/messageTimestamp.ts
@@ -7,13 +7,28 @@ const DATE_WITH_YEAR_FORMATTER = new Intl.DateTimeFormat(undefined, {
 });
 
 /** Time only for today's messages; older ones lead with the day and month. */
-export function formatMessageTimestamp(input: string, nowMs: number = Date.now()): string {
+export function formatMessageTimestamp(
+  input: string,
+  nowMs: number = Date.now(),
+  timeFormatter: Intl.DateTimeFormat = TIME_FORMATTER,
+): string {
   const timestamp = Date.parse(input);
   if (Number.isNaN(timestamp)) return "";
   const date = new Date(timestamp);
   const now = new Date(nowMs);
-  const time = TIME_FORMATTER.format(date);
+  const time = timeFormatter.format(date);
   if (date.toDateString() === now.toDateString()) return time;
   const sameYear = date.getFullYear() === now.getFullYear();
   return `${(sameYear ? DATE_FORMATTER : DATE_WITH_YEAR_FORMATTER).format(date)} ${time}`;
 }
+
+/** `is24Hour` overrides the locale's hour cycle with the system clock preference when known. */
+export function createMessageTimeFormatter(is24Hour: boolean | undefined, locale?: string) {
+  const timeFormatter = new Intl.DateTimeFormat(locale, {
+    hour: "numeric",
+    minute: "2-digit",
+    ...(is24Hour === undefined ? {} : { hourCycle: is24Hour ? "h23" : "h12" }),
+  });
+  return (input: string, nowMs?: number): string =>
+    formatMessageTimestamp(input, nowMs, timeFormatter);
+}
diff --git a/apps/mobile/src/features/threads/useMessageTimeFormatter.ts b/apps/mobile/src/features/threads/useMessageTimeFormatter.ts
new file mode 100644
index 000000000000..2320d369762c
--- /dev/null
+++ b/apps/mobile/src/features/threads/useMessageTimeFormatter.ts
@@ -0,0 +1,22 @@
+import { requireNativeModule } from "expo";
+import { useEffect, useMemo, useState } from "react";
+import { AppState, Platform } from "react-native";
+import { createMessageTimeFormatter } from "./messageTimestamp";
+
+function systemUses24HourClock() {
+  if (Platform.OS !== "android") return undefined;
+  return requireNativeModule<{ is24HourFormat(): boolean }>("T3NativeControls").is24HourFormat();
+}
+
+export function useMessageTimeFormatter() {
+  const [is24Hour, setIs24Hour] = useState(systemUses24HourClock);
+  // oxlint-disable-next-line t3code/no-unreasoned-state-sync -- Refresh the native clock preference when Android returns to the foreground.
+  useEffect(() => {
+    if (Platform.OS !== "android") return;
+    const subscription = AppState.addEventListener("change", (state) => {
+      if (state === "active") setIs24Hour(systemUses24HourClock());
+    });
+    return () => subscription.remove();
+  }, []);
+  return useMemo(() => createMessageTimeFormatter(is24Hour), [is24Hour]);
+}
diff --git a/apps/mobile/src/lib/filePreview.test.ts b/apps/mobile/src/lib/filePreview.test.ts
index 8363b0ba5c95..2c7a7313e47e 100644
--- a/apps/mobile/src/lib/filePreview.test.ts
+++ b/apps/mobile/src/lib/filePreview.test.ts
@@ -113,6 +113,7 @@ vi.mock("../components/ui/Button", () => ({
     createElement("button", { onClick: props.onPress, disabled: props.disabled }, props.label),
 }));
 vi.mock("expo", () => ({
+  requireNativeModule: () => ({ is24HourFormat: () => true }),
   useEvent: (_player: unknown, _event: unknown, initial: unknown) => initial,
   useReleasingSharedObjectWithLifecycle: (
     lifecycle: {