Sounds like your mind's pretty much made up! I'd pick the lesser of two evils if I were you (i.e. the 7:30am time.)
My test was at 8am. I showed up around 7:30am; the security guard of the building was super friendly and told me a couple of jokes to try calm my nerves after I signed in. I sat down at the lobby to review some notes (there were other people there studying for their exams), and around 7:40am, someone from Prometric came to bring us up to the testing center. They gave us some stuff to read about testing policy, etc., and then we had the chance to put stuff away in our lockers/go to the bathroom/whatever before we signed in to take the test. They check your sleeves, the insides of your pockets, and make you roll your pants up so they can see your ankles before you go into the testing room. The whole process was pretty quick; I think I started the test right around 8am.
Just a warning: if you decide to bring one of those wraps/sweaters that extends past your butt, you might not be allowed into the testing room. I only say this because they didn't let a woman with a longer sweater enter the testing area the day I took the test. They also scan you with one of those handheld metal detector thingies every time you go back into the testing room, so make sure to make time for that on your break.
