No matter what the reasons given for being late to class, you are still late. Why? Showing up on time is discipline and martial arts is a discipline - and when the most basic, entry-level, self-discipline requirement is not met, it sets the stage for other areas of errosion.
I understand traffic problems, illness etc...and arrangements can be made with the instructor if it's going to happen on a frequent basis.
I also agree that attending some part of class is better than no class. But, I just think a very sincere effort should be made. After all, a dojo doesn't really have to accept you as a student. It is a priviledge.
been there/done that