The Sander amp(s) have reputation for great sonics and run cool so can be left on all the time. It seems like I've read even with his they can improve over 24 hours which is why he recommends leaving them on.
Amps with short warm up time 4 critical listening
What class A or AB SS mono block amps with min. of 300w per ch. have a very short warm up time to sound it’s best for critical listening? I’m talking about less than one hour. I have a pair of Pass Labs xa160.5 class A amps which take a couple of hours to warm up for critical listening. During that time of warm up I play music at moderate level but I don’t listen to it until it’s 100% at its peak of performance.