my test started at noon, but i went the day before to check the center out and the girl working there told me you can basically start whenever you get there, if you like. it seemed like you can come early, but not late.
hopefully you won't have the same situation i did... even though the testing center is open until basically the last tester leaves, pretty much everyone else in the building leaves around 5 so they turn off the a/c then. 😡 i started noticing in my last couple of sets that it was really getting awfully warm... especially since here in tx it's been about 90+ degrees every day as of late and since i'm usually cold in air conditioned rooms, i dressed to prepare for that. another thing you might have to be careful of... one of my friends was also taking the exam at the same time and on his last break he went outside to eat a snack... since it was after 5, the doors were locked and he couldn't get back in! luckily the attendant heard him banging on the window and let him in.