I leave solid state parts of my system on 24/7 and I can hear a difference if unplugged for a bit to swap something out and then replugged. It really takes a full day to get everything sounding good again, especially toroid transformer gear. That's not scientific, just my experience. Tube gear sounds good after an hour but great after two or three so I turn it on when I walk in the door and then by the end of dinner, listening is wonderful.
