This is behaviour caused by the audio engine, as it deliberately keeps the machine awake. You can imagine that Cubase users would prefer the machine to not go to sleep during a recording session.
We’re considering ways to make this optional for Dorico users.
Yet, I also have “Sleep” set for 2300 hours. So I launched Dorico a few minutes before, to see if the iMac would honour the sleep schedule and, lo and behold, it did!
So, it’s only the energy saver that the Audio is keeping from kicking in, not the Sleep schedule.