Personally, this is my protocol with an all solid state system. Always on: streamer, DAC, preamp (Pass XP22). Turn on when wanting to listen: amp (JC5).
If I want to critically listen, I try to turn the amp on in advance but to me I don't notice a significant increase in sound quality with the amp cold or warm. Certainly nothing to warrant leaving it on 24/7. I only turn everything off when I'm out of town for extended periods, and the most noticeable component that needs warmup and time to sound its best is definitely the XP22.