I have the following setup:

<telerik:RadTimePicker x:Name="picker" MinuteStep="5" SpinnerFormat="HH:mm"/>

When opening first time the picker already shows time for example 11 : 00

So I did not change the values of hours and minute and clicked OK . The Time property reflects data as 11 : 21 (current time on device ) instead on 11 : 00 which is confirmed by clicking OK.