No time, in fact I don't even allow anytime to get to work early. I have a 14 minute leeway where I can clock in without needing approval. Only takes me 5 minutes to change a flat tire, but I don't carry a flat kit on my commuter bike since my route is so short. Strangest thing is that in 8 years of commuting to work I have never gotten a flat on my to work, it was always on the way home.