[Mathew_M]

I find late night listening always sounds best. Could be less noise in the power or state of mind. I once read that being a night owl, after everyone is in bed is akin to flying in a hot air ballon. Never flown in a balloon but I get it. Too bad I can only afford to stay up late a couple nights a week.

[Mike-48]

I agree with others that there may be many reasons, but one is constant change in our minds and emotions. Are you always in a receptive state for anything? For better or worse, I'm not. I find the same thing even at live concerts. Even the best ensemble won't captivate me on some days as much as others. Is it the playing, or is it me?

A recent thought is that perhaps we respond differently to imperfections in our audio systems differently at different times. Removing as many as possible could make our responses less variable. I have a highly treated room, but I was sometimes bothered by a high-frequency echo. When I killed that with an absorber, I found I enjoyed the music not just more, but more consistently.

[dallaire1]

A really good Indica and the M3's go amazingly together. I live in Arizona.

[whydontumarryit]

A really good Indica and the M3's go amazingly together. I live in Arizona.

Aahh. Problem solved. I should have realised I was just complicating things. 

[ajaye]

If you think about the way your hearing threshold for level is able to adjust over a short period of time based on how soft/loud you're listening, it's reasonable to assume that there are also changes that can happen day-to-day/at a macro level as well...but I have no evidence on this so consider it a theory.

Also, temperature in the listening environment absolutely plays a role. For one thing, don't fire a register right into a speaker's path during heating season.  Clearly shown why not here in this video. The scenario is extreme for the purposes of demonstration, but the fact remains.

https://youtu.be/_lB8e9OY0-U

PS Dave is a live sound legend and did a ton of these videos over the past year+. Most are from the perspective of reinforcement but many of the principles and topics are still useful for home/hifi.

[Letitroll98]

Last night, I cut my system on and let it warm up for a while prior to listening. When I was ready to listen, I turned up the volume and it sounded sluggish initially. I realized that warm-up has to occur at the listening level. Otherwise, it takes about 20 more minutes to warm up if the volume is lower at the onset. Is that inexplicable? I dunno.

Once the system warmed up, it was the most glorious sound I ever heard.

I've found this especially true with components using SMDs, they really need signal going through them to warm up, usually around 20 minutes as you mentioned.  Perhaps others may have an idea of why this is so.