I am trying to plan my training for the next year with the intention to systematically train for the first time.

I “trained” 650h in 2019 and about 450h this year. However, not systematically and with many mistakes, mainly spending way too much time in zone 3.
Realistically, I will have about 8h per week available for training next year. Reading thru the Uphill Athlete book all training plan suggestions have some kind of progression.
My question is, how do I manage a progression in training volume of my available times is limited to about 8h per week.
Do I start with a much lower volume than I did in previous years and increase towards 8h, in which case I would initially decrease volume, or do I train at a a constant time volume, in which case I don’t have much of a progression?

Thanks in advance.