As far as I'm concerned I am being paid for a service which is paid for in a particular amount of time.
I am clear in my advertising about the type of services and experience offered. I also guide clients in what I can/cannot do. Two hours of constant shagging away, with no breaks or orgasm for the man, that is not the sort of thing I'm offering. I have had someone do that but it's very rare.
When I offered half hour bookings I found many of them did want to cram things in, or saunter around making 30 minutes into 50 minutes.
I have however also had several men book 1 hour, over run, and then saunter around and when I've said something about their 1 hour becoming 90 minutes, they have taken offence. Interestingly enough several of these told me they considered me friend, and that they cared for me, often they'd be on a regular discount or old rates. It's not logical that they'd then test my hospitality, or perhaps that's the whole point!
Other times I have clients who book the time they know they will take up, and go bob on that time which is absolutely brilliant.