This is a whole topic of its own. There is a lot of great discussion on incorporating outdoor riding into your cycling plan here:
in general, consistency is the cornerstone of a successful season of training. How restricted will you be on the busy weeks?
If you can still get three days of riding in on your busy weeks, I would recommend selecting a low-volume training plan so that you can always complete your scheduled workouts. Then, on weeks that you have extra time to ride, you can do additional outdoor rides to increase your overall riding volume for that week. This also gives you the chance to enjoy some unstructured outdoor riding, which can have a positive impact on your morale and motivation over the course of the racing season 
Happy training!