I'm sure they just take it down until store hours in the morning...give the inventory guys at each store time to count the days shipments and upload them to apple.com. As sophisticated as you might think it is, they still have to do a manual count too....and also make the cute little cards they hand out to line waiters...
They used to do online reservations back in the iPhone 4 days, and you could hang around the store at 9pm because they'd release the phones that weren't picked up by 9, and if you knew an employee or just engaged one they'd sell it to you. Managers would say if someone is willing to buy something that we now have available to sell, go right ahead.
Don't know if that still applies, they used to use the genius bar reservation system for that. Now they might just put the left over phones into their counts for the next day. But if people who reserve get a time limit, and it's say 9pm and the store closes at 9:30 that leaves a half hour window to check and see if anyone didn't pick up their phones.
