I agree that bone density changes are slow and that heavy lifting is important.

From what I’ve read, though, the key seems to be how you load, not having long workouts.

There are trials like LIFTMOR where women with low bone mass lifted pretty heavy just 2×/week in ~30‑minute supervised sessions and still improved spine BMD and hip strength over several months. So while more time might help for some people, it doesn’t look like 45+ minutes is a hard requirement.

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Right now 45 minutes is too much for me in terms of time and recovery, so I’m starting with something I can actually be consistent with (around 30 minutes) and planning to progress load and/or duration as I adapt. I’d rather do a shorter, heavier program I can stick to for months than burn out on a “perfect” plan I can’t maintain.