For example, if a program prescribes 30 minutes steady state 4x/week, are there meaningful differences in adaptation if one instead did 40 minutes 3x/week, or 60 minutes 2x/week, etc., assuming total weekly MET-Minutes are equivalent?
We don’t really know, as frequency usually affects volume. In general. While I would prefer that people are active on most days and that most conditioning bouts are at least 15 to 20 minutes long, I don’t think there’s a huge difference in a day less or day more until volume starts getting much higher and/or there are some higher stress conditioning workouts that should probably be more isolated.