On outcalls I do set an alarm on my phone. I say, "Let me just put my phone on silent." I put it in airplane mode and then set the alarm. I set it for exactly the time they've paid for, starting from that moment. So, the initial couple of minutes and hello kiss aren't counted. I'm not dead set on being out the door within the sixty minutes, but I won't go beyond the time they have paid for.
I am going to look for a pretty, delicate watch to wear when I'm next on tour as I generally like to keep an eye on things so that I can see how they are progressing. This can work in their benefit, as well: if the between-pops chatting looks like it may be going on too long a glance at the clock will remind me that it's time to initiate a second round.
I understand that clients may hate that we watch the clock but you will notice that they do, as well: some of them feel mighty cheated if they leave in 45 minutes. I am just careful to respect their money as well as my time and I will never indicate that they ought to leave until their time is up.
I will go overtime when I feel like it. That is my prerogative.