The main theme of a time-goal program is recovery. If you build enough rest into your program before you need it, your body will be continuously recovering, rebuilding, and adapting for the performance demands of your goal. By preventing extra fatigue and taking extra rest at even the first hint of slower recovery, you can maintain a steady performance increase without being forced to take a week or more off because of injury or over training.
Learn more about  time-goal programs in Jeff’s book Marathon.  You will find the book at:  https://shop.phidippides.com/collections/books-dvds