Figure that you normally get to work at least 10 minutes early and stop for a coffee while you change and cool down. So if you get a flat, you're still on time, if you skip the coffee and change fast.

There's also the question of how often. Workers occasionally arrive late because of a traffic tie up, car breakdown, mass transit delay, or some kind of family emergency. If you get a flat and show up late once in a blue moon, you're probably still below par.