forgo daily

I have a 9 o’clock class today. I got to class at 8:58, and the professor wasn’t there yet. Someone said that he missed a flight and was running late. So, we waited. At 15 after, I mentioned something about the rule. See, there’s this ‘rumor’ that has always gone around about a 5- or 10- or 15-minute rule, where basically if the instructor hasn’t shown up in that amount of time, then you can leave. I tried to look it up in the university documentation, but couldn’t find anything about it. Well, today a girl said that if the prof has a doctorate, then you have to wait 15 minutes, otherwise you only have to wait 10. She seemed confident about what she said, but does that make sense? Waiting longer for a doctor? Is it assumed that a doctor has more important things to do than a non-doctor and is thus justified in being later? I don’t know. I’m sure it will continue to be a mystery, to me at least.