Android TimePicker ignores 24 hour system setting when using Format Property - fix (#28797)

### Description of Change

More generic condition for detecting the 24 hour date format

### Issues Fixed

Fixes #28784

Author: kubaflo

src/Core/src/Handlers/TimePicker/TimePickerHandler.Android.cs

@@ -156,7 +156,23 @@ void OnDialogDismiss(object? sender, EventArgs e)
 			HidePickerDialog();
 		}
 
-		bool Use24HourView => VirtualView != null && (DateFormat.Is24HourFormat(PlatformView?.Context)
-			&& VirtualView.Format == "t" || VirtualView.Format == "HH:mm");
+		// "HH" (uppercase) is the .NET 24-hour specifier; "hh" (lowercase) is 12-hour.
+		// Case-sensitive Ordinal comparison is required to distinguish between them.
+		internal static bool IsCustom24HourFormat(string? format) =>
+			!string.IsNullOrEmpty(format) && format.Contains("HH", StringComparison.Ordinal);
+
+		bool Use24HourView
+		{
+			get
+			{
+				if (VirtualView is null || string.IsNullOrEmpty(VirtualView.Format))
+					return false;
+
+				if (VirtualView.Format == "t")
+					return DateFormat.Is24HourFormat(PlatformView?.Context);
+
+				return IsCustom24HourFormat(VirtualView.Format);
+			}
+		}
 	}
 }

src/Core/tests/DeviceTests/Handlers/TimePicker/TimePickerHandlerTests.Android.cs

@@ -11,6 +11,24 @@ namespace Microsoft.Maui.DeviceTests
 {
 	public partial class TimePickerHandlerTests
 	{
+		[Theory(DisplayName = "IsCustom24HourFormat detects HH patterns correctly")]
+		[InlineData("HH:mm", true)]
+		[InlineData("HH:mm:ss", true)]
+		[InlineData("HH.mm", true)]
+		[InlineData("HH-mm-ss", true)]
+		[InlineData("hh:mm", false)]
+		[InlineData("hh:mm tt", false)]
+		[InlineData("h:mm", false)]
+		[InlineData("H:mm", false)]
+		[InlineData("t", false)]
+		[InlineData("T", false)]
+		[InlineData("", false)]
+		[InlineData(null, false)]
+		public void IsCustom24HourFormatDetectsCorrectly(string format, bool expected)
+		{
+			Assert.Equal(expected, TimePickerHandler.IsCustom24HourFormat(format));
+		}
+
 		[Fact(DisplayName = "CharacterSpacing Initializes Correctly")]
 		public async Task CharacterSpacingInitializesCorrectly()
 		{