About 30 to 40 minutes.
20 minutes unless I’ve had a call from them.
Well, that depends on the situation and on whom I am
meeting. I would usually wait if the person calls or texts me to inform that
he/she is on his/her way. Otherwise, I would wait for around 20 to 30 minutes
and call. If he/she does not answer, I would try again after 15 minutes and
Up to 45 minutes, depending on the person's track record for being dependable. If it turns out to be anything other than an unavoidable emergency, I will have learned my lesson and won't wait for them again. (People who are close to me know that promptness is a big deal to me. I don't keep people waiting if I can avoid it, and I expect the same courtesy.)