How early should i get to the harry potter 7 part 2 midnight premier?

okay so I already have my tickets, so that isnt a problem. and i didnt think seating would be a problem either.... but i was talking to my friend whos going to see it in 3d and shes going 6 hours early to get in line to make sure she gets good seats. how long should i get there in advance? i mean i already have my tickets, but is it necessary to be so early? i mean im not gonna walk in at midnight, maybe 30 or 45 minutes before. is that alright? how early should i get there