It depends on the imaginations of both you and the other party, as well as the mood you are in, your relative interests etc.
With some people - as with the parlour girl who once asked me 'why would you want to book a whole hour ' - even a shorter time can be too much.
When I was younger and living in London, I had a few good overnights (and 'over days') with various EE regulars with more intellectual interests, generally shag, see a show/gallery etc, dinner, imaginative role play+shag, sleep a couple of hours, shag. In part where it worked, it worked because the girls were actually interested in going out and doing what we did, and as such the charges were reasonable.
It really comes down to this, in the time you are together, what do you personally have fun doing that you think the other person is also going to be able to maintain interest in to such an extent that it's worthwhile paying what you are paying (whether that be some kind of role play, swing club, etc).