You can not paste a correct time (which match the correct format, like: 11:30:15) in a timebox if the timebox has no previous time setted.
It's happen only when there no value set previously in the timebox.
Try the behavior here : http://zkfiddle.org/sample/2vmlqme/1-BUG-timebox-paste
Or simply try this zul :
<label value=" 1 - Input a valid time here, and copy the value (CTRL + A and CTRL + C)"/>
<label value=" 2 - Try to paste here"/>
<button label="3 - Click here to lose focus of the second timebox"/>