I have a 12.5 mile commute. Here is the routine:

5 AM - get up
5:15 - on the road
6:10 - arrive at work
7:00 - on duty.

I leave early, because I have to be at work at 7 am. If I am late then someone can't leave. I am a little paranoid about a flat, so I allow a lot of time. I could leave later, and if I had a problem, work would come and pick me up.