UTime was made back before XGUI was even a sparkle in Stickly's eyes. Also, like most other official UProducts, UTime was written mostly with support in ind for Sandbox and Sandbox derived gamemodes.
Mmmm.... Sparkles... (drool)
I think the reason we really haven't made UTime XGUI compatible is because it does not depend on ULX whatsoever- you can use UTime without having ULX or XGUI installed. However, there's no reason we can't have it detect if XGUI is installed. Or even easier, we can just create the XGUI module for UTime, and it'll be ignored if ULX isn't installed!
.. Thinking about how trivially easy this would be, I really want to do this now. My problem is finding a large enough free chunk of time..