Some days I only have time to do a 40-45 minute ride (I won't say how far I go). In fact, I do a lot of these, during the week, before work. I beg to differ that you need to ride an hour, especially if you are just starting, or you are doing intervals. The rides I do in these short amounts of time always involve 1-2 big hills, so, for me, it might be equivalent to riding for say, 1.5 hours of flat to rolling terrain, in terms of the energy I expend. When I first started cycling, I had a 13 mile training route. It really was sort of flat, but again, I did it after work 2 times a week. My other rides were longer and more traditional, but those little rides got me going and built up my mileage. I ramped up very quickly, from this, going from a first ride of 6 miles to 20 miles in a short time.
Now, 12 years later, I just accept the fact that I don't have time to do 30, 40, 50 mile rides all of the time and I try to make the most out of whatever I do. The goal is to have fun.