Currently it’s not possible in a straightforward/user friendly way. If you could make a GitHub issue for us that would be great!
Temporarily I think it might be possible if you desperately need this now. I believe we have periodStart/periodEnd on the context variable passed to the painless script which is the time interval that the monitor should be running at. You could do a comparison against this to ensure it only runs at your desired times. Again, not a great solution, but something that can unblock you. Ideally we will add a feature that lets you disable it during certain timeframes.