I tried to reproduce the described behavior, but to no avail. Could you please elaborate a little bit more on the presented issue. Please let me know, which version of Prometheus controls are you using. Pasting some code form the TimePicker declaration will be helpful. Also why do you need to change the ID of a control? Note that this reflects the control tree of the page and you might get corrupted ViewState.
All the best,
the Telerik team