I did something similar in recent weeks by my usual routine was 2xthreshold and 1 O/U supplemented by 1 Z2 ride. I come from LV and whole 6 months of cycling so this was virtually a bump from LV to MV in terms of TSS.
My TTE was 45 min and my progression was:
3x15, 2x20,3x20,2x30 (with added time in Z2 at the end) ,1x60 and Gibraltar+2 at the end. I could handle this without much of a problem. My TSS was on level with MV but with 3-4 workouts a week. The O/U were the most taxating for me. I have not done any VO2 max work during this block.
Now after recovery week and small bump in FTP I am starting new block of these. But doing 4x a week a threshold workout seems pretty “hardcore”.