You did not give your age/fitness level. As a graying engineer I like having a safety margin. I have had 21 mile commutes (each way) and allowed 2 hours each way at the start. Took 1:41 in the summer heat. Later a 25 R/T commute took just over 2 hours total, half the way in the dark. The first two replys give very respectable times that I would love to work up to if I did not have so much urban traffic to deal with.