My t has never been more than 2 or 3 min behind and even that is very rare so my answer is hypothetical. I probably would have checked the appointment card in my purse to make sure I had the correct time. If there was a receptionist there at that time I would have asked after 10 min. of waiting. (Sometimes there isn't a receptionist during later appointments.) If after 20 or 25 min there was no explanation from t or the receptionist for the delay, I would reschedule with the receptionist and leave. I sometimes have to rearrange my work day for appointments so I can't always wait around. My t is very firm with the ending "time" boundary in appointments, so I figure I have the right to be firm with starting time boundary also. If it turned out to be an emergency of course I would be understanding when I got that explanation.

As to what I would say to t, I am not sure. I am sure I would feel angry at least part of the time but I have a difficult time expressing anger with t. A lot of my response would hinge on the explanation for the delay.