Shaving your legs doesn't take much time at all. I race a few times a week (during the season) and shave once, at most twice, a week. Probably takes 10 minutes to shave. There's nothing I could do for 10 minutes a week that would improve my time by up to eight percent (most amateur cyclists already overtrain as it is). Not part of your question, but shaving is also largely about being able to treat road rash and avoid infection.