I'm personally trying to avoid running the heat pumps (mini-splits) during the coldest part of the 24-hour cycle, because the colder it is outside, the more energy required to produce the same amount of heat.

So I've been turning them off when I go to bed, and then trying not to turn them back on again until mid/late morning when it's had a chance to warm up outside or at least the sun is on the compressor. It's close enough to the bedroom window that I can just hear it in the silence at night, and it's the sound of money being spent.

Many would argue that you shouldn't adjust the setting on heat pumps at all, but just leave them. I don't quite agree with that, because the same heat is more or less expensive during the colder/warmer parts of the outside day, and my home cools slowly enough that I can meaningfully average those.

But I would argue against turning up heat pumps "for comfort" during a particular part of the day, especially if that's a time when it tends to be cold out, like first thing in the morning - so for someone who's leaving the house to go to work or school, trying to wake up to a warm space is fairly expensive.