Time of Day for best Sound

@ghdprentice - same here. Night time. I live near a fairly busy road and definitely the reduction from traffic vibrations makes a difference. However, I think another factor is the power amps being fully warmed up. Even with Class A amps, it takes them a full two hours to sound their best.

@cdc 

Finally, someone says something that makes sense to me. As air density changes so does its acoustic impedance. As temperature decreases the acoustic impedance increases. Sound needs air molecules to translate from source (speaker) to receiver (ears). Ever hear the statement "in space no one can hear you scream?" This is why.

High humidity sucks the life out of the sound in my experience. Hence I use a dehumidifier to keep humidity at 40 or below. That makes a lot bigger difference in my house of stereo than time of day.

My experience mirrors that of @ghdprentice and @yoyoyaya, and this has been quite consistent over the years, with Sunday evening after 9pm being absolute prime time. Seems the result not just of lower in-home power competition, but of neighborhood generally, plus lowering of ambient noise floor, e.g. vehicle traffic. Perhaps most of all, brilliant engineering for a local NPR music program, so good it justifies using a Magnum Dynaco analog tuner. I generally follow this program with a streaming session, and there too the sonic results are optimal for the week.
Whatever the time of day, I am using AQ conditioner with customized DH Labs Red Wave power cable. If Sunday night performance can be duplicated on Friday afternoons by switching to Furman Elite as @erik_squires implies, I will gladly trade in the Audioquest . . .
 

Night time is the right time, especially for FM radio.