We're hoping to do opening at 8:30 or 9, then keep opening short to get moving early. You'll want enough time to check in, set up any gear, go through safety, and costume up. Early is better, as all if this will take longer than you think. If you're NPCing, setting up NPC camp and briefing takes up some of that time instead. If you can get there by 6 you're probably in good shape, after that might feel rushed.