Is there any danger in leaving a class D amp on unattended for ten days?

How can you be sure an amplifier really does sound better when left on? Human sonic memory is not more than a few seconds, so you can only know if you compare two identical amplifiers, one left on for a while, and the other started from cold. To be honest, if there really is a difference (which in most cases I doubt), it would be a bad design.
Apart from the two disadvantages I already mentioned (fire risk and harm to the environment) there is of course another one: heat is the enemy of electronics. Leave your gear on and you will significantly reduce the life span of critical components.

no way to know for sure, no way to prove...just an impression from using the same gear for a bunch of years...I do a combination of on, standby, unplugged depending...though I am more inclined to leave the amp on during this Arctic blast, less so in summer...

willemj

Human sonic memory is not more than a few seconds ...

While auditory memory is shorter than visual memory, to suggest that auditory memory lasts for just a few seconds is an oft-repeated claim by audio measurementalists such as yourself. Oddly, I've never seen it accompanied by any documentation. Do you have any to offer?

Leave your gear on and you will significantly reduce the life span of critical components.

Nonsense. There is plenty of audio equipment - and other electronic components - that is rated for continuous duty. My ARC SP-11 preamp was left on essentially continuously for decades without issues. I sold it to a friend a few years ago ... it’s still running like a charm! And that’s a tube-based component.

The main factor affecting longevity and reliability of passive components is power/temperature cycling. So excluding infant mortality and external interferences like lightning, etc., leaving the component on should not negatively affect its longevity. As to whether or not it sounds better when left on, let your ears be the judge.

Apart from the scientific articles that the ordinary Audiogon user does not have access to, here is the wikipedia article on auditory/echoic memory: https://en.wikipedia.org/wiki/Echoic_memory