I think a lot of agencies and massage parlours advertise an 'unrushed' service and maybe are somewhat to blame for clients pushing the limits were time is concerned?
I recently worked for a short time in a parlour and the 'unrushed service' was always quoted and impressed upon a potential client. Also there wasn't a clock in the room although I got rather good at knowing when the half hour was up.
If I did go over, sometimes by 10 or 15 mins if the client was taking his time, the receptionist(usually the owner, a previous wg) wouldn't knock on the door unless another client was waiting!
Funny how quickly she changed her tune when she wasn't the one lying on her back for free