Steps to Reproduce

1. Turn the "Use 24-hour format" device setting off on your test device
2. Create a TimePicker
3. Change the format sometime later on (e.g. when the user clicks a button)

Expected Behavior

TimePicker displays time in new format

Actual Behavior

TimePicker still displays time in original format

Version Information

Xamarin.Forms 2.5.0.91635

Proposed Fix

I can see the problem in Xamarin.Forms.Platform.Android.TimePickerRenderer. The format is cached in OnElementChanged then never gets updated. Presumably, the format just needs to be refreshed in OnElementPropertyChanged if FormatProperty has changed.