I would say that your training schedule will to some extent be dictated by your current fitness levels and training volume. What is the longest ride you have done to date? How many times/week do you ride?

I ride a lot, but this time of year, it is definitely a challenge to stick to a training schedule. My first race of the season is also April 11. I am using it as motivation to stay in shape during the winter. My race is short (30mi), so distance isn't an issue, but power and climbing is.

In your case, if you can't ride outside, but are training for distance, you will need to log lots of hours on the trainer. If you don't have a solid base, just do long slow distances (LSD) for a while to get ~500mi under your belt. If you have a base already, you can do intervals to build power/speed and keep it interesting. Maybe a couple of longs days each week and a couple of interval days, and a couple of days off. I would usually say to include an active recovery day, but with riding on the trainer being so dull and at the same time mentally challenging, I would say to take a few days totally off the bike. Maybe mix in some cross training like x-country skiing, snow-shoeing, or swimming.

Also, will your race have a lot of hills? Do you need to practice climbing? If so, simulated climbs on the trainer, and intervals will be a must. Finally, if your goal is to win, you will have to focus some time on building power not only for climbs, but for a finish line sprint!

And find training partners if possible. It is soooo much easier to do a trainer ride with the motivation, and healthy competition, of other people.

Good luck!