We all have a sense of how long our commutes should take after we do them a couple times, even if we choose to take a new detour; time estimates are of limited use to us. I think google maps might be tuned to give estimates for bike tourers because it is probably a lot more important to them. You're far more likely to do only 10-12 mph on a loaded touring bike and doing day after day of 50-150 miles.