I checked google maps against my daily commute. Once I dragged the map line to the streets I actually take (I ride an extra half mile to get a wider street with less turning traffic conflicts), the distance and time were very accurate. My bike computer tells me I average 11.0 to 11.5 mph for most of my commutes, and that is rolling speed (not including time stopped), so when I add in a couple of minutes at some of the 10 traffic lights I ride through, the google time estimate is pretty accurate for me. Higher speed riders will get there earlier, obviously.

Just be sure to take the suggested route as a starting point and look for safer nearby alternate streets as alternates.