I was just saying on another thread that distributors often don't send the books out to the stores until release day, to be sure that they're NOT put out early. The delivery trucks have a certain route, and they do try to get to stores very early, but stuff happens and SOMEONE has to be at the end of the route.
Plus, the stockers are supposed to be in early in the morning, but sometimes...yeah. Stuff happens there, too. It will still be the same book at 5pm (and that's REALLY LATE for stockers, by the way) s at 10am. Patience, grasshoppers