Since I started training for racing in 2007, I have done periodized structured training for road and track. Endurance training was/is determined by the length of the individual events and/or the number of stages in an event.
If I do all the structured work I have to do plus the strength training, I am fortunate if I have enough energy for z2 endurance riding. And the structured part of the workout generates a lot of endurance and increased aerobic capability. So all I have to do is add enough additional riding to tolerate the duration of the event and recovery between workouts.
Today, we are doing preparation which is focused on strength training and short sharp efforts on the bike with not much riding. This afternoon, I did a track workout with a warm up, jumps and 4 sets of 2 flying 100 meters and 1 flying 200 meters with rest between sets and efforts.