Have you ever hated the sound of your system one day, and loved it the next?

I think the biggest difference is YOU. Depending on how much dopamine you have floating around up there at any given time can influence what you are hearing tremendously.
I think the time of day/pressure/humidity/weather can play a role, but not as much as above.

Often. It is a holistic issue involving different levels of water intake, daily life experience, media format, speaker position, chair position, humidity, how many things are on my mind, what I had for my meals, first/last CD or LP chosen that day, etc. etc. etc. could it be my electricity? Sure, that too.

Often I will just find that LPs don’t sound good, or CDs don’t sound good. Rarely it is both not sounding good. Perfection is when both sound good equally. 

It is is important to both quantify and qualify/externalize and internalize our audio experiences. But we should never take it too seriously—unless it is our profession. If it isn’t your profession, I think it a good idea to turn it off and go for a walk. 

Excellent post!

"Funny you should ask."
https://www.youtube.com/watch?v=jHelEOHjtH4 and the link to the article; https://www.stereophile.com/content/magic-moment 

I call it when your system has a cold. Maybe dirty power. Could be some static in your cables. Humidity levels is another factor. I control the humidity in my music room to 45-49 percent.