I'm no expert, but the first step in any training program is base building. It isn't complicated, just a slow build in mileage from week to week, with one long ride a week. Don't expect to build every week, take a step back every 3 weeks or so to let your body absorb the training. It takes patience, so it is a process I struggle with. My solution was to hire a coach. He writes out my schedule and keeps me out of trouble, since my tendency is to overtrain. I have trouble with the concept that I can't build every week, that I can't build every sport at the same time, and I can't race hard at every race I want to go to. That's not unusual.
Be sure you are training in an aerobic zone, which is slower than you think. Get a heart rate monitor to keep yourself from going too hard. Speed and hard workouts should wait until your base is secure, and the base it the largest part of your training. You are looking at 38 miles, very doable in the length of time you have. That's no sprint distance, so remember your aerobic system is the one to hone for endurance.
Above all, have fun! Spinning around your world is enlightening and enjoyable (especially once the weather gets warmer!) Racing is fastastic, but the key is to enjoy the training.
I don't know if that is any help, and I'm sure others have more info. Joe Friel's book is great for training, but a little overwhelming for me. There are plenty of online training schedules for running, I wonder whether there is a schedule out there for building a cycling base?