In pre-base recommendations include a variety of workouts within your currently selected focus duration (Athlete type). If you want to mix things up more change focus type or use Filter to do that on-the-fly.
If you move the TED closer (starting at 120 days from now) you will initiate progression but as noted you can stretch out the phases if you want.
My first TED this year is April 4th after which I will float for awhile in post-event (similar to pre-base) then decide whether you want to set another TED in the fall and begin another round of progression. In this case though you already have a solid base built so you don’t need to start over in Base phase. You could go right to Build by setting TED 75 days out. I am starting at a higher level of fitness and building upon that. Well, at least trying to. 
Also consider how you want to use IR which isn’t just hours but moderates intensity.
The higher the ramp rate the harder the training load. You can use IR to ramp up and down to emulate that 3 weeks on, 1 week off approach, or leave the rate lower and slowly progress stretching phases by manipulating TED.
Think of it as steps where you control the how steep the steps are, how long you climb at that pitch. and when to take a breather before you start climbing again.
For more on the traditional 3 on/1 off approach vs Xert see this thread:
Xert training schema, rest weeks, etc - General - Xert Community Forum (xertonline.com)