Well, 2:45 seems like a pretty good time to do it. Its after 2 am, so almost everyone who was out that night has gone home, and its not early enough for them to be getting people in for pre-work breakfast. Between 2:30 and 3:30 seems like it would be the best bet, by far.

I dont know if every McDonalds is 24 hrs anymore; I havent eaten McDonalds in months. As the gay weightlifter mentioned, it would probably be up to the manager of the individual McDonalds, as most of them are franchised and there really wouldn't be any enforcable corporate policy about this. But if you order at the box and dawdle a bit, your food should be ready by the time you go to pay with your unusable credit card, and what are they gonna do, throw the food out? Perhaps, but you have a good chance of getting your hands on it pro bono.