I work at a Gamestop and how we do it is, is you come in during evening and we give you a finalized receipt and depending on if the company sends us merchandise, we give out raffle tickets and start giving people merchandise. At 12am the doors are open and you just stand in line and trade out your receipt for your game. As for what time you should go, I would just call the store and ask them what kind of a line they are expecting. They usually have a pretty good idea of how many copies they have paid off.
I have a question, I already paid mine off, will I still need to get a finalized receipt? I didn't know how it worked so I WAS gonna show up ten or fifteen minutes before Midnight. Will I not be able to do the latter? I live in a small town, population anywhere from 30.000 to 50.000 and my gamestop has around 200 pre-orders. Thanks
Edit I meant small county of 30.000-50.000
