Training by time is a good way to start off... I would suggest that you start off riding three, maybe four times a week. One time a week do your "long" ride. Aim for an hour and a half on the long ride, and see how far you go. That will also give you a little something to measure yourself by as you get stronger and start improving... you can go farther and farther in your 90 minutes because you're getting faster, and not getting so tired, either...

I end my Road I classes with a little quote from 5x Tour winner Eddy Mercxx, which goes something like this: "Ride as long as you want to, or as short as you want to... and as fast as you want to or as slow as you want to... but go out and ride!"

Tom