My daily z4 is two blocks of 15 minutes with 15 minutes of high cadence z3 "break" in between.

Twice a week, I do 1 hr 15 minutes z4, no breaks preceded by 45 mins of two z3 blocks and one z4 block for warm up. All this, indoor training. I feel I can still do more time but free time is pretty limited.

I have two rest days a week which may include a lower back massage from mom Massage helps a huge deal. My lower back can be in pain and after the massage, it's mostly gone.