Amp — Leave on or turn off

I tend to lean towards leaving things on, and digital/transistor for sure.

I think what the manufacturer recommends is irrelevant.  What matters  is your own ears, and your willingness to pay the electric bills. :D

If you can't hear a difference, leave your gear off.  If you can, leave it on.  It's that simple.  No measurement is going to tell you any better.

RV, I have repeated your experiment a number of times with the same results. On longer always sounds better, but with diminishing returns, for about a week.

Its’s true of my DIY phono/pre - it’s on all the time. It’s true of my DIY Class A amps (they idle continuously at half power). It’s true of my Bryston SST in the HT (although B recommends turning it off). But since HT doesn’t matter nearly so much, I do turn the B off, and then back on an hour before - but an hour isn’t really enough.

My cartridges take 10-40 minutes too.

As for the car analogy, I ALWAYS used to warm up my engine carefully, and my tires too, before taking a fast lap.

YMMV

I had a Krell FPB 600 amp that I always left in the standby mode until I powered it up to listen. Was doing that for years and years. Then I have now the ARC Ref 750s. And I always let them warm up about 1 hour before listening. Happy listening. 

Class D / on 24/7

Class A / off

RVPiano - are you aware the Benchmark can be set for auto shutdown 

after 45 minutes of sensing no audio signal? Also the Benchmark handbook 

states that due to the SMPS power supply the amp is at its full potential the moment it is turned on.