How early should I show up for the double feature of Harry Potter and the Deathly Hallows?

I've got tickets for six people, including myself, to go to the double feature of the Deathly Hallows on the 14th. Part 1 doesn't start until 9, but what time should I arrive to get in line for that one? It most likely wouldn't be as crowded as the line for just Part 2 will be.