Mine stay on for months at a time and I use them daily. If it were a system with infrequent use, I would power down. With my main system, I power down when any cable switching or speaker swaps occur. Turn off thumps and meter lamp replacement are minimized. If there was any noise when amps idle, it would be noticed immediately because it's normally dead silent.
Come to think of it, it's time to put the PM-1.5 back into the mix. Thank-you and welcome to the fold.
Welcome @DaveyDick