If you want to keep it even simpler for even stupider, then just two rules are enough:
- Do as much volume as possible.
- Within that alloted time do as much intensity as possible, while still being able to recover enough/not overtrain.
For those with plenty of time that might be lots of longer Z2/S1 sessions with just 1 or 2 shorter harder sessions per week. While for others with little time that might be 3 shorter hard sessions and only one longer Z2/S1 session.