At MIT, lectures must follow MIT time; all lectures are expected to start 5 minutes after the hour, and end 5 minutes before. Funnily this means each lecture is about one microcentury long. Exams are the one exception, they start on the dot.
It'll say 10:00 c.t. on the event, meaning it actually starts at 10:15.
https://en.wikipedia.org/wiki/Academic_quarter_(class_timing...
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.
A microcentury is 100 nanoyears if you prefer that.