When we first see the stage, there are three lights at the top: two to the left, one to the right. But after Fry says "these guys rock harder than ever", we see them again and there is one to the left and two to the right. Then the camera angle changes, and again we see two to the left and one to the right.
Ad-Rock's 5-o'clock shadow disappears in his close-up.
The clock outside Sparky's Den says it's 8:30 (and doesn't have a millennium count) when Bender says "I'll just be a minute"; four seconds later, it says it's 8:00 (and does have a millennium count). Fry also waits till 11:20.