A lot of the class D (non pro stuff), says "Leave it on". In the summer anything with valves gets turned off.. 15-30 min in the summer time for a tube preamp to warm up.. An hour in the winter though.. I like 60 degrees in the winter, with valve amps and valve preamps.. It takes about 30 min, if I played them the day before..(winter). The speakers sound better on cool crisp days, too.
Regards
Regards