The base/build/specialty, followed by a “rebuild” of redoing the build/specialty plans, is a common approach to peak for multiple events.
However, from the sound of it, you have exactly one goal event, so you don’t need to peak for a race and then recover and repeat. In that circumstance, and knowing that you’re trying to maximize your sustained power for somewhere in the range of one hour… I’d recommend the other common approach for filling out that much time: lets of base.
Starting with traditional base, you can do I, II, and III in 12 weeks before your 3 week holiday. That is a lot of low and slow work, but it should do wonders for your aerobic conditioning. To change things up and subject yourself to different stimuli, you can follow that up with Sweet Spot Base I and II, for a total of 24 weeks building a monster aerobic engine. However, at that point it’s probably time to change up stimuli again.
After that I would try to do an extended Sustained Power Build of 12 weeks (do the first 4 weeks, then do the first 4 weeks again, then do the last 4 weeks), include a couple weeks of buffer to rest and recover as needed, and then do the 8 week 40km TT specialty plan.