In the morning: 8 miles, about 35 minutes. In the evening: 8 miles (unless I opt to take a longer route): 40 minutes...this tends to be cause the wind is always in my face on the ride home and it's pretty darn strong.
I was trying to estimate this morning how much time I waste at stop lights, as I hit quite a few of them on my way in. If I hit every single green light, I could easily shave off 5 or 6 minutes. This is of course on the commuter bike (old mountain bike, steel, 40 pounds + gear). When I ride the road bike I'm sure it'll be less (havent done it yet)