Most guys will know when their time is up but for the odd one or two that like to linger, there are ways of moving them on without standing up and saying time to go. If there time is up ask politely if they would like to extend rather than jumping up and telling them to go (sounds silly to have to say but it seems a lot do actually do this).
Apologies if I've told this story before, but it's relevant. My first ever punt was for an hour starting at 1pm and by the time all the directions had been adhered to ("park there and call me", "well I'm not in that street I'm in this other one", "park at this other place then walk to here", "and don't make it look like you're using your phone", "now go to the green door", ...) it was 1.15pm when I was in the door. The punt proceeded until about 10 to 2 when the girl announced that time was up in 5 minutes unless I wanted to extend the appointment by half an hour. Despite being a nervous novice I explained that I didn't arrive until 1.15 due to directions not being given until 1pm and then she said she could not carry on past 2 because she had to go out shopping (even though she had been willing to extend by half an hour if paid...........).
How not to win repeat business.
We don't like being short changed on time, we don't like being given hassle over directions - a full postcode without house/flat number is the minimum before the punt, most of us hate extras being charged and if they have not been publicised in advance that's deception. We don't much like being told that shower time must come from within the appointment time, unless you are joining us in the shower - we like to believe the time we've paid for is all sexy time, not necessarily an hour of pounding, though.
Anyway this is now turning into one of those threads we've already had on here about advice for WGs, so I'll stop there!