I abandoned the Zwift TT tune up plan out of a lack of faith in the people who wrote it, and lack of flexibility of 100% indoors only workouts to the tune of 6 per week. You simply can't have someone do 4 intensity workouts a week with one day off.

So, I wrote a crap ton of custom workouts. Sweetspot. VO2. Under overs. 3x8's. Etc....

Did my own under over workout of 3x9's with 2min under 1min over. I typically prefer the "over" to be a hair higher than most plans do, and the "under" a bit lower than the plans do. I feel injecting a bit more lactic or whatever in that minute to clear in the subsequent 2min raises the bar more than barely moving the needle like the Zwift workouts do. I wrote it so you would have to do 3x9, with an optional skippable rep at the end of each set to make it a 3x12. Just swipe right if you want 3x9's. Don't for 3x12's.

Did the 3x12. Was good. It hurt.