My Pass Labs XA-60.8 mono blocks are class A and leaving them on would bankrupt me :). But they have a standby mode. They warm up fully after about 30 minutes. Like others have stated, it’s amp specific. If you change to another amp, consider one with a standby mode.
Amp — Leave on or turn off
I always turned my Benchmark AHB2 amp off after use every night. After all, why is there an on off switch on the front panel if not to do that? Last night I accidentally left it on. This morning, when I played my first record, I couldn’t believe my ears. The same record I played last night sounded infinitely better. I tried a second record and that, too, was much better.
I know there’s a debate on the question of leaving an amp on all the time.
I now know where I stand!