I always look at the time when i hear the knock on the door, that way i know exactly when my time will be up. Being mostly a one shot guy (unless the chit chat was super short and she got my very exited fast and i came without being able to hold it) i usually manage to finish with way over 15 mins left. Then its a bit of cuddling and/or talk before she goes in the shower by the 6/7 min left mark. But it happen sometimes we chated a bit too much (even after 10 years i still need to correct myself on that departement) and i finish very close to the end. I apreciate an alarm BEFORE time is up, that way i can finish. Happened a few times the alarm would start when i was very close and they always let me finish (took 1-2 mins max)
I know some clients abuse the time, so i don't blame SPs for being "clock watcher". But i also agree with Fradi that if nessessary, an extra 5 mins shouldn't be denied, it can make a big difference into a session for the client. The keyword is not making it a habit and trying your best to stay on time.
At least doing mostly outcalls like i said i know i can start the timer when she knock on the door, and i should have my full hour minus 5 to 7 min for shower time, then its up to her to speed shower if she feel she need to, as for me its no issue at all if she goes over time if needed. I had an indy once who stayed like 15-20 min over time because she had a diner and needed to redo her make up and prepare (we had agreed for a COF finish lol) .
But anyway to go back on topic, i don't really know whats really a "clockwatcher". The real definition would probably be someone looking at the clock often, wich make you feel like she really don't wanna be there. But even myself i look at the clock ocasionally to be sure to know how much time i have left, i try to do it discretly and im sure SPs do the same, but i got "caught" a few times and i caught a few girls too doing it, but like once so its no big deal.
As for cutting time earlier (like having 15 mins left and she want to end it there) thats not clockwatcing thats litteraly stealing time you paid for... And cutting you when your time is up is fair game for her, altough like i said if the guy is wanking super fast and is about to cum, this may not be the best business decision to do it.