My answer? I don't. The only exception being physicians I *know* are
running late because they are spending needed time with patients. I had
an ENT who would come in at 6:30 and 7AM to see patients before they
needed to be at work, he would also fit in all emergency cases that
day. His office would be very up front when you arrived for your appt
that Dr. P was running behind and gave the choice to wait or
reschedule. I didn't mind because I knew that if *I* was the patient in
need he was available for me.

Now I had (note the past tense) a GP who had prominently displayed a
paper at the front desk that if you were 15 minutes late for an appt
the appt was automatically canceled and you had to reschedule. Fine.
Except when I had the first appt of the day the doctor was 1 hr late.
Nothing said to me from her secretary. No opportunity for ME to
reschedule. She comes in and flippantly says her child had an ear
infection. Nifty, next time MY child has an ear infection and I'm an
hour late for my appt will you wait for me?
Total and complete lack of consideration for MY time but I'm supposed
to respect hers? Don't think so.