DISCUSSION: "It only comes out at night". Does anyone else have this experience!?

70% of our brains processing power is occupied with vision. At night we need way less for vision, and that brain-CPU time (aka attention) is available for hearing. 

Also, at night the background noise floor drastically drops, and you can hear 20-30dB lower detail levels than during daytime. Add that to multiplied attention level due to vision placed on standby.... 

Now, that is coupled to much less strain on the electrical grid. Consider that what we hear as music is the electrical grid driving your room acoustics. The music software is just the recipee... the raw ingredients are line AC + room acoustics, so what came in goes out.

So yes, at night we have drastically different internal and external environments compared to daytime.

Clean power

peak low to med listening levels between 10pm - 4am. 
 

As with most things audio it is not any one thing but rather a bunch of them all together that makes the difference. Try coming home at 2AM firing your system up cold and see how it sounds. So one reason it sounds better late at night is it always sounds better after being run several hours. 

All components are highly susceptible to vibration. One source of vibration is cars and trucks, wind, and even trees. Wind blows, trees move, roots transmit vibration into the ground. This all tends to die down and be less at night. Best of all is a fresh blanket of snow. So, vibration.

Then there's electricity. Pretty much everything running puts a bit of back EMF onto the line. Every wire is also an antenna bringing RFI noise into the system. A lot of RFI sources tend to be off late at night.

The validity of some of these effects is easy enough to test and verify. Vibration? Pods and springs work, and the sound in the afternoon with a calm fresh blanket of snow is at least as good as late at night if the wind is blowing. Leaving everything on and playing after you got to bed, you will hear almost all of that great late night sound the next day. So this proves the warm up effect. RFI? Disconnect a lot of wires by flipping circuit breakers. It will sound in the middle of the day about as good as late at night.

I only have this problem when I'm not using my Furman power conditioner with LiFT and SMP

My system sounds best late at night, Sunday night in particular. I have noticed this for decades in different states. I am sure it is a quieter power grid. While I have a good quality power conditioner… the noise floor still drops late at night.