Right now, I'm 2 miles from work; when the temps get a bit more agreeable, I'll open up my 'alternate routes', which are anything from 3 to 9 miles one-way. All depends on my mood, and I KNOW, with the idiocy I'm dealing with already this year, that I'll NEED a little stress relief!
A few years ago, my commute was a solid 9 miles one way, daily; did it as quickly as 32 minutes, and as slow as 55, depending on weather (the 55 was in January, 5deg F/-35F windchill and sleet). If I do the 9-mile loop I have laid out now, it's a little under 40 minutes.
BTW, I ride a Kona Coiler, about 36-37lbs. I have a tendency to get silly on a whim sometimes, can't ride the lightweight stuff....