I would only expect to get the time I've paid for. 1) both punters and WG's alike often say we (the punters) are paying for the WG's time, not the services, so to expect to get longer for the time paid, is a bit hypocritical, and 2) In my job, I expect to only be there for the time I'm being paid, so why should it be different for the WG?
I have one regular I go to see, that time is not an issue. I don't pay at the beginning of the meet, she asks me how long I'm thinking of staying, to which I usually reply 30-40 mins, and often it ends up being an hour, sometimes more. Never does she look at the clock, or remind me of the time, and leaves it entirely up to me to get dressed and make moves to leave. When I do, I ask her what I owe her, and she reminds me I'm on "VIP rates" and then makes up a number that's lower than her normal rate anyway. Seems to work for both of us.
But I fully understand, and respect, that a WG can, and will, draw the line when the paid for time is reached. Thankfully it's never happened to me; I've either finished just before the time, or if we have run over, it's only been by a few, maybe 5, mins, and it's been fine. Granted, I may feel "hey, come on" or "little bit cold" if a WG was to say to me "right, that's the hour up" or whatever, but she is entitled to do so.
And I'm sure all of use, at one time or another, have been kept waiting by a WG for an appointment, which is probably caused by a booking overrunning. And I for one would rather wait that extra 5-10 mins while she showers than steam into the appt on time, without her showering. I put in the effort to be clean and smell nice, and I expect the same in return.