Basically, this part of the logic should be handled by custom code. One option would be to directly assign the value to the TimePicker, which can then try to parse the value.
Altertnatively, you can use client side code, to validate the input, before assigning it to the RadTimePicker. How you parse the value, however, is up to your requirements/logic. Other than the built-in client side methods to set the value/time/date, there is no other api to help in this direction.
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