Cajones of steel

How late is it acceptable to walk into a class? I know that I'm probably more sensitive about these things than other people are, since I run my life by the ticking of the second hand on the clock, but can we agree that there is some point when it is just rude to enter class after it has already started?

I'm not begrudging people the ability to come into class a little bit late. We've all had days where we overslept our alarm, caught every single light on the drive to school as a red, or took just a little too long in the shower that morning.

This morning in my Federal Courts class (which is 50 minutes long, meets in a small classroom, is a seminar class so small that the professor takes attendance usually just by looking around and knows all of our names), a certain martial-arts aficionado/former cult-member who makes his children partake in crazy family rituals came to class late.

Class begins at 9:30. He sauntered into class at 10:11. When there are only nine minutes of class left, is it really justifiable to walk into the room? At that point, wouldn't you just call it a missed class and take the additional nine minutes to ease the rush of the morning?