It's certainly been my experience that noisy AC lines are a culprit for variability in sonics along with warm up time. With all my gear over the years 1 hr seems to do it for warm up benefits...more just doesn't help much for my ears. But the time of day has huge sonic swings and compelled me to eventually get a PS Audio Power Regenerator. It even measures the distortion coming into the unit and I can see it go from more than 4% THD during peak area usage periods down to 2% late at night or very early in the morning. With the regenerator the output is consistently below 0.1% THD which has seriously enhanced my listening experience. Plus it regulates the voltage to a consistent 120V....otherwise mine fluctuates 118-123V otherwise throughout the day.
Amplifier warm up
I was plalying Boz Scaggs, "Silk Degrees" LP. After side one, I ate dinner. One hour later I played side 2. The second side sounded clearer, more vibrant with better sound stage. I have a Parasound P6 preamp and Parasound Halo A21+ amp. Is it possible that an hour of warm up improved performance?