My Ayre V-5xe Amp on/off switch (front of amp) is really an on/stand-by switch. (The actual on/off switch is on the back of the unit.), which implies that the electronics have a low wattage draw that keeps them 'warmed' and ready when I 'turn on' the front switch.
That being said - I agree that morning listening is markedly better than at other times. Line -noise? Low Humidity? Rest? Sum of all...?