There is so much debate about this because powering on is probably the hardest thing you can do to tubes. Personally I always turn mine off when I am finished listening for the day but leave on as long as it is possible I WILL listen. So approx 4-8 hrs on days when I listen to music on my system (not every day). I would think that if you spend significantly less time listening than not listening turning off is a good way to go. My amp is also class a so it is always full power all the time. So that is a factor for me.
