There's a thread on this in the 33 with different viewpoints. The concept is that you build a broader aerobic base over the winter, then decrease volume and increase intensity based on your priority races/events. The aerobic base gives you a better foundation for the intensity later on. Riding more slowly =/= taking time off. You're riding at your normal endurance pace, the pace you hold when you go out for a solo 3-4 hour ride.

For context: I just finished my first (ever) block of base. The riding durations during those three weeks were 18:30, 16:30 and 13:30. The next block will be similar. This isn't all JRA; one of the long days each week includes 3-4x20 minute intervals at just under FTP. After that block, I'll be going to gradually shorter, more intense workouts. My first race is mid-February, my first priority race is March 9, so my base period is completed two months before my first race and three months before my priority race.