"But it sounds better at night...."

A well-traveled topic that I raise yet again.  On the "are power regenerators snake oil" question, the response that has made most sense to me is: No, if you have some material issue with the power supply coming into your home.  If you live in an area with what I will call normal modern power infrastructure, and have quality components, you will probably not notice a difference.

But I live in a city, do not suspect any power problems, and feel with a pretty high degree of certainty that my system sounds better at night.  This is a common sentiment, attributed to more activity on the electrical grid during the day.  Can these two positions be reconciled?  Why DOES the system sound better at night to me and many others?

Is our perception straight-up wrong, and the result of some bias or non-auditory reason why listening at night is a better experience?

Maybe when listening at night, one average for most people, the system will have been on longer, and therefore be more warmed up?

Is our perception real, and supports the proposition that baseline electrical system usage does materially affect many systems, and you don't need a clear power "problem" to benefit from a regenerator? 

Let's rehash it all again gentlemen!