Yes you can set it in the code-behind. You just have to use:
|timepicker.SelectedTime = null;
There is an issue with the SP2 dll's that If you have set time and then set SelectedTime
to null, next time when you open the pop-up it will look visually as you have selected time, although the value is null. This is also fixed and will be available in the next weekly build.
the Telerik team