The reason for keeping the amp on all of the time is to keep its temperature at its optimum for the performance of the amps thermally sensitive components. Turning it off for a few moments or hours shouldn't make a meaningful difference. FWIW, the only reason to leave it on all of the time is to avoid having to wait for it to warm-up to its optimal temperature. This should never take days to achieve, especially once you are past initial breakin. Hours perhaps. The reason most keep them up 24/7 is it is thought that there is no downside other than the nominal cost of the electricity and that maintaining the temperature might cause less degredation than the continual process of heating and cooling. With high power amps biased heavily into class A I'm not sure about the extent of thermal related degredation due to being left on constantly.