I've gone to several midnight releases in the southern US and the only time it was reserved seating was for IMAX and I don't think they do it anymore (also Fandango effed up and we had handicap seats which were an empty square to put a wheelchair in. Needless to say, we skipped that showing ) The most other theaters have done is tell people to move towards the middle of the row because it was going to be a full showing and there couldn't be any seats between people.
I would definitely go ahead and buy your tickets online though if you haven't. That way you know if it's reserved seating or not and also so you don't get there and they are sold out. Went to see the first Avengers movie with some friends and they tried to convince me and my bf that we didn't need to buy tickets in advance but good thing we did because they had sold out signs up when we got there.
It mostly depends on where you're seeing it. If it's a major city, then an hour ahead should be fine. A more local place, I would say maybe 30-45 minutes ahead. You'll be standing in line regardless so make sure you wear comfy shoes or whatever. Hope you and your friend have fun I personally love the experience of a midnight release.
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