Overtime on talks

From http://ift.tt/1wRAOMd:

Your talks should be clear, concise, fun, exciting, and never ever run over time. For each extra minute your talk runs over, 10% more of the audience will decide you are a jerk and start fantasizing about you falling down a trap door.

After 11 minutes, 110% of your audience will start hating you.

That makes perfect sense, because that includes the people waiting for the room to open up for the next talk to begin.

But some people at my college like to take the opposite view. One lecturer never releases his class until he's run at least five minutes overtime. In the mandatory presentation class, the teacher maintained that going five minutes over the twenty minute talk period time was ok, but when one student went one minute undertime, she insisted that he repeat the assignment.

My question is: how should the speaker treat overtime?