Comment by BearOso

At a US university, I had an large elective class where the professor refused to start until things had "settled down", and he said he was going to add that time to the end to ensure he got his full 50 minutes.

I had a major-related class 10 minutes after, clear across campus, about a mile of walking. This professor was nice about it, but I was the only one coming in late at all.

So I made sure to sit in the front row of the earlier lecture, and left precisely when the class was supposed to end, leaving no doubt I had places to go.

Some people just think they set the conventions.