Generally the clock starts the moment you step through the door.
A SW that knows their business has worked out the science of the pacing of a booking and will have something like a music list or something to act as subtle reminders for them.
So yes, walking through the door is on the clock, getting to know you chat is on the clock, having a shower before getting into the action is on the clock, doing the do, having a breather and if you're able doing the do again is all on the clock, as is having a second shower.
Essentially no 1 hour booking is 1 hour of bonking, it is a parcel of time in which all the above happens.
In other words if you're walking out the door within a few minutes (either side) of 1 hour after you walked through the door, then you have had a 1 hour booking.
If you are going through an agency, and you're sure that your booking was cut short without an excuse or you choosing to leave early, then contact the reception straight away, but be sure that you're right, because they'll almost certainly have evidence of when you entered the premises and when you left, so they'll know.