If you enter a format with a 24 hour time( Format="dd MMM yyyy HH:mm:ss") for the Timepicker
If you enter the same format for the DateTimePicker the TimePicker in the DateTimePicker looks like this:
It seems like this is a bug as the only way I can change the DateTimePicker time UI is to alter my language/culture whereas the TimePicker displays correctly based on my format.