Because that's when your Imagination works the best ...
I wish it was my imagination. For 15 years, 80-95, I was a high-end dealer. Every day was the same. During daytime hours, I got a headache listening to the system, nightime a whole different story.
I tried SS amps, tube amps,line conditioners,over warm sounding speaker wires, everything. It practically drove me nuts trying to solve this problem.