You can make an appointment for any time, even early morning. Just email the lady or ladies you like, choose one, and agree on a time. They will prepare and be ready for you, even if it is early morning.
GFE date, no you cannot take the lady into Vegas, or anywhere else. The ladies are not allowed to leave the premises.
If you don’t make an appointment, what time to show up? As I understand it, the ladies are assigned to either the day shift, which I believe runs from 5am to 5pm, or the night shift, 5pm to 5am. However, the few times I have been there, you won’t find many ladies hanging around the bar before noon. You can show up anytime and ask for a line-up, but if you want to just mingle in the bar and choose a lady that way, I would say mid-afternoon to about midnight, you should have plenty to choose from.