That 1 to 8 change happened to me, too! I was so angry. I found that if I was camped out with my info entered in and hovering over the time I wanted, I could get tickets while in Hawaii at exactly 3 PM (I did this twice successfully while we were there).
There are bathrooms, and they're even kind-of close to the entry, but I don't know what time is "early." I do know you cannot take any kind of bag in - not even a small purse - and you have to put those in your car or in a storage locker.
Whatever happens, good luck. It's a must-visit place.