Another data point: (I checked the source code page yesterday before the ID numbers were made invisible.)
Two reservations placed on same transaction in store 3/31 about 10:12 am Pacific (13:12 EST) in Southern Calif, about # 30 in line when store opened.
Credit card was charged almost immediately.
Email took until 2:38 am the next morning to arrive.
Numbers are both 500xxx and are three digits apart.
From reading comments on this thread, I'm guessing my relatively high numbers are because a backup server was handling some orders at the 10 am west coast crunch time. There must have been a rush of order activity right at that moment, considering that west coast is such an EV hot spot.