It was these vagaries that I was thinking of. I agree that each team’s warmup time, pre-game shows, etc are tightly controlled. But if the celebrity singing the N.A. decided to hold a note a little longer, or drops his mike on the way to the field, then you’d get mis-timings.
So to recap, from the information provided by David Simmons and caligynephobia (afraid of pretty women?), we get: jet circles at some IP, say 10 miles away–which at 300 mph is 2 minutes away. Pilot gets a countdown at 2 min + (say) 30 seconds. Pilot times his circling during the countdown so he hits the IP at zero. Which means the contact on the ground has to know when we are 150 seconds from the end of the N.A., which could only be derived from rehearsals with the singer (one supposes).
Pretty cool. Thanks, all, for clearing this up.