Tweek tells the boys that the Under-pants Gnomes only come out at 3:30 AM. When the gnomes steal the guy's under-pants at the mayor's office, it is broad daylight.
No, no, no! Tweak said the underpants gnomes come to his bedroom around 3.00am to 3.30am, he wouldn't know where else they go and at what times. The underpants gnomes could go anywhere at anytime but goto Tweak's house at 3 to 3.30am.