It depends on the area and the provider and schedule.
As for area, I am not going to sit in my car in a residential area for more than a couple minutes without getting out. So if three minutes goes by after the appointment time/my contact saying I am there, I just take off. In a busier area I would sit maybe 10 minutes at most before moving on. In that case, I would typically contact her after five minutes and say I am leaving in five. Then I would leave if I do not hear from her by then. Often at that point they say give me a minute and then five minutes later they are ready. In either case, if she got back to me within 15 minutes after the appointment time, I would probably head back and do the appointment.
As for the provider factor, I have headed back when a provider was 30 minutes off, but she had a good excuse and I really liked her, and I had time. But I don't think I would head back for anyone after 30 minutes.
As for schedule, I think it is fair to build in 15 minutes leeway to allow for error, but I don't think anyone should expect someone to build in more than 15 minutes. And, I think if you cannot respond until even 5-10 minutes after the appointment, then you should understand if the other person bails. If I am going to be one minute late I make contact before the appointment time with my ETA, offer to take a shortened visit (so pay regular rate and end at regularly scheduled time), and then live with the outcome.
So bottom line is that I think 5 minutes is fine, 15 is safe. If someone is going to get mad like I was supposed to wait for more than 15 without hearing even an excuse for the lateness, then it is probably good avoidance
Luckily this is not really an issue and usually works out for the best. Now, this does not solve the issue of the certain someone who claims she will "blacklist" you if you cancel within 2 hours before an appointment and than "blacklists" you anyway when you cancel more than 2 hours before the appointment, but again, good avoidance.