Some leave early, some leave late. It balances out eventually.

I have a timed playlist from as soon as they walk in the door though  No obvious clock watching.

...obvious holding back or showing no signs of wanting to wrap things up with 5 minutes to go (I had one of these the other week on tour who wanted to discuss other positions we could try at the 57 minute mark) or otherwise deliberate twattery and they're done no more than a minute after their time's up.

Oh how I loathe this. Just had one of those today. Just come already you greedy fu*k...

Personally I have always, since day one (been at it two years) timed it from as soon as they walk through the door.
Saying that, I have always worked for agencies, so, especially regarding incalls, I have no other choice, as it's their apartment, and if one person runs over it can unfairly screw up potentially another 15 ladies days.
 However, I wouldn't do any different if I were to ever actually get a none time wasting AW booking after 3 months & 70+shitty messages go independent.
 I provide a very vanilla service though, and I find due to my age (20) that I tend to get a lot of boundary pushers. It has got to the sorry point where I have to repeat myself to a lot to clients when they try and force me into services I don't provide (OWO, A levels etc.) that they are paying for my time not my what happens within it.
 Don't get me wrong- I have no problem staying for longer with outcall clients who I actually enjoy the company of. I have stayed for a good 4 hours extra with some clients (just talking) who I actually really 'click' with- but they're never first time clients & they know me well enough not to try anything beyond the paid time. But that is very rare.
 When I enjoy someone's company & conversation & have nothing better to do with my day I will stay as long as I want to unpaid (again, no sex involved beyond the paid time) but I always make it very clear that is my choice on this occasion and it may not happen again.
 However, as most people on this forum will be aware of by now, I am constantly struggling for money due to terrible bad luck with attempts at going indie and every agency I have worked for being heavily bent on favouritism, so if I do stay with a client for longer than what they've paid for it's mostly because I am so bored/lonely that I actually crave the company...

I do outcalls only at the moment and I start the clock (my internal clock) from the time I walk in the door. An hour is more than enough to include pleasantries and chatting, and they're already showered when I arrive. Sometimes I will stay a little longer.

From the time I open the door, the time starts. I'm fairly lenient with time and not a clock watcher (I don't own a watch and never have my phone out), but guys are usually very respectful of time. I've never had it run over by more than about 5/10 minutes.

I will let sex time overrun 5 mins on half hr bookings and 10 on 1 hour bookings. I do have a visible alarm clock but I don't see why I shouldn't as I need to know what is the time and I don't keep glancing at it, eg  when I get the condom or toys I will check it. Also most guys take their watches off or don't wear one so it gives them an indication of how long they have left and I see them look at it.

I talk too much sometimes so spend too much time chatting even on half hr bookings but I am going to stop 

Clearly charge him for 30 minutes and he has to go after 30 minutes.
Cant charge a client for one hour if he is late and you have another booking right after, you have the option not to take the late client at all or to leave at least  one hour between bookings.

Its how I do it and never had issues.

I dont time my bookings anymore, I have an internal clock built in. I dont mind if they stay 10-15 minutes longer, especially if Im enjoying myself. I always take at least one hour break between bookings or more and I dont like to see more then 2-3 guys in a day. I know its shocking, but I preffer to stay sane and dont burn out.

+1 this is exactly the way I work.

I never really "time" the booking, I just kind of know how long it's been. I may check now and again and sometimes the client actually asks me too, but I'd never clock watch. I don't mind going slightly over, I never include the shower in the time. With playlists etc it seems very rigid and parlour like to me, I think some guys actually (excuse the pun) "clock on" if you do that, not wrong but not something I would ever do.

Don't get me wrong, I wouldn't let someone take the piss, but then all my clients are generally very nice and leave pretty much on time. I also never see more than 2-3 max guys in one day and always leave at least an hour (usually much more) between any booking.

I start from when they walk in, or whatever time the booking was scheduled to start - so if it was 2-3pm it starts at 2pm. if the client is late then tough, but if I am late then obviously I will run over as it was my fault.