So I went to the Apple store today to talk to a sales rep to try and get more info. She said that there's a morning and an afternoon shipment of iPhones everyday. The morning shipment is available to the public when the store opens, but the afternoon shipment isn't sold in the store and is held for reservations at 10PM-4AM.
I'm not sure if this is accurate, I'm just relaying it. She also said they didn't get any Verizon iPhone's today from either shipment.
I doubt that this is true for every location. If it is then the shipments must be very small otherwise people would be having better luck reserving phones at 10pm.