No pause.
UTime, at least Megiddo's original version, and I presume every other "improved" one made after, uses
oldtime + playerleft system time - playerjoined system time.
There is no timer other than the computer clock.
(The currently only way) I imagine you could prevent idlers from being counted would be similiar to what UTime does now.
Keep a running cumulative variable of a players afk time during the session.
Then actually modify the sh_utime file function, likely the GetUTimeTotalTime to subtract totalidle of the player.
oldtime + playerleft system time - playerjoined system time - session_afk