From 91dfd5c2394c70c12fbb08cc5a6684098e70afb9 Mon Sep 17 00:00:00 2001
From: Akash Santra <santraakash999@gmail.com>
Date: Mon, 27 Apr 2026 02:21:28 +0530
Subject: [PATCH 1/3] fix: incorrect 24h time detection for non-AM/PM locales

---
 packages/lib/timeFormat.test.ts | 40 +++++++++++++++++++++++++++++++++
 packages/lib/timeFormat.ts      | 16 ++++++-------
 2 files changed, 48 insertions(+), 8 deletions(-)
 create mode 100644 packages/lib/timeFormat.test.ts

diff --git a/packages/lib/timeFormat.test.ts b/packages/lib/timeFormat.test.ts
new file mode 100644
index 00000000000000..4a81d6d8194625
--- /dev/null
+++ b/packages/lib/timeFormat.test.ts
@@ -0,0 +1,40 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+vi.mock("@calcom/lib/webstorage", () => ({
+  localStorage: {
+    getItem: vi.fn().mockReturnValue(null),
+    setItem: vi.fn(),
+  },
+}));
+
+import { isBrowserLocale24h } from "./timeFormat";
+
+describe("isBrowserLocale24h", () => {
+  beforeEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it("returns true for 24h hourCycle", () => {
+    vi.spyOn(Intl, "DateTimeFormat").mockImplementation(
+      function () {
+        return {
+          resolvedOptions: () => ({ hourCycle: "h23" }),
+        } as any;
+      } as any
+    );
+
+    expect(isBrowserLocale24h()).toBe(true);
+  });
+
+  it("returns false for 12h hourCycle", () => {
+    vi.spyOn(Intl, "DateTimeFormat").mockImplementation(
+      function () {
+        return {
+          resolvedOptions: () => ({ hourCycle: "h12" }),
+        } as any;
+      } as any
+    );
+
+    expect(isBrowserLocale24h()).toBe(false);
+  });
+});
\ No newline at end of file
diff --git a/packages/lib/timeFormat.ts b/packages/lib/timeFormat.ts
index 4864df4119b7bb..9998a8d17045e3 100644
--- a/packages/lib/timeFormat.ts
+++ b/packages/lib/timeFormat.ts
@@ -41,14 +41,14 @@ export const isBrowserLocale24h = () => {
   } else if (localStorageTimeFormat === false) {
     return false;
   }
-  // Intl.DateTimeFormat with value=undefined uses local browser settings.
-  if (!!new Intl.DateTimeFormat(undefined, { hour: "numeric" }).format(0).match(/M/i)) {
-    setIs24hClockInLocalStorage(false);
-    return false;
-  } else {
-    setIs24hClockInLocalStorage(true);
-    return true;
-  }
+  
+  const formatter = new Intl.DateTimeFormat(undefined, { hour: "numeric" });
+  const hourCycle = (formatter.resolvedOptions() as any).hourCycle;
+
+  const is24h = hourCycle === "h23" || hourCycle === "h24";
+
+  setIs24hClockInLocalStorage(is24h);
+  return is24h;
 };
 
 /**

From b8d9bf9f67d64ff578b1e7b386f924750a186cb1 Mon Sep 17 00:00:00 2001
From: Akash Santra <santraakash999@gmail.com>
Date: Mon, 27 Apr 2026 02:32:57 +0530
Subject: [PATCH 2/3] chore: improve test typing for Intl.DateTimeFormat mock

---
 packages/lib/timeFormat.test.ts | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/packages/lib/timeFormat.test.ts b/packages/lib/timeFormat.test.ts
index 4a81d6d8194625..6e1a4f77e52670 100644
--- a/packages/lib/timeFormat.test.ts
+++ b/packages/lib/timeFormat.test.ts
@@ -16,11 +16,11 @@ describe("isBrowserLocale24h", () => {
 
   it("returns true for 24h hourCycle", () => {
     vi.spyOn(Intl, "DateTimeFormat").mockImplementation(
-      function () {
+      function (): Intl.DateTimeFormat {
         return {
           resolvedOptions: () => ({ hourCycle: "h23" }),
-        } as any;
-      } as any
+        } as unknown as Intl.DateTimeFormat;
+      }
     );
 
     expect(isBrowserLocale24h()).toBe(true);
@@ -28,11 +28,11 @@ describe("isBrowserLocale24h", () => {
 
   it("returns false for 12h hourCycle", () => {
     vi.spyOn(Intl, "DateTimeFormat").mockImplementation(
-      function () {
+      function (): Intl.DateTimeFormat {
         return {
           resolvedOptions: () => ({ hourCycle: "h12" }),
-        } as any;
-      } as any
+        } as unknown as Intl.DateTimeFormat;
+      }
     );
 
     expect(isBrowserLocale24h()).toBe(false);

From 634524dffb2f5b978539e30386e6c1480c5bc311 Mon Sep 17 00:00:00 2001
From: Akash Santra <santraakash999@gmail.com>
Date: Mon, 27 Apr 2026 02:38:43 +0530
Subject: [PATCH 3/3] chore: replace any cast with narrower type for hourCycle

---
 packages/lib/timeFormat.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/lib/timeFormat.ts b/packages/lib/timeFormat.ts
index 9998a8d17045e3..a3fb70569abcf5 100644
--- a/packages/lib/timeFormat.ts
+++ b/packages/lib/timeFormat.ts
@@ -43,7 +43,7 @@ export const isBrowserLocale24h = () => {
   }
   
   const formatter = new Intl.DateTimeFormat(undefined, { hour: "numeric" });
-  const hourCycle = (formatter.resolvedOptions() as any).hourCycle;
+  const hourCycle = (formatter.resolvedOptions() as { hourCycle?: string }).hourCycle;
 
   const is24h = hourCycle === "h23" || hourCycle === "h24";