Warm-up time for amps and preamps

10-15 years ago had a sound engineer come to my home and plot frequency response with MLSSA software, using test tones and sound level matched by meter. Repeated 5-6 times over the next 3 hours with the differences clearly notable on the visual graphing. Nothing subjective about it so far. Did those differences translate into different sound? Yup. Did I perceive those differences as qualitatively desirable? Yup. This on an all SS system left on 24/7, unless I will be absent for 2+ weeks. Just for the fun of it we repeated this on my and a couple other systems a few times. Same result without respect to components-visually represented differences in response over time, some more so than others, but none stopped changing within our 3-4 hour window of trials.

Oops, premature send. I meant to end by saying that in many instances we continued to see visually represented change long after we believed we heard any additional changes.

Fsilahua...Is SO CORRECT!!  as stated SS equipment has no warm up time.  As with tubes some equipment (not so much with audio) has a low voltage standby current that keeps the filaments warm so as to diminish the start up time when the equipment is turned back on. 

And contrary to popular belief, just because you do not "feel" the amplifier is getting warm, does not mean the buried components on the PCB are not under a lot of stress do to heat and current.  Components fail do to this factor, and to leave your equipment on 24/7 is ludicrous.  Yes there is voltage spikes, but the engineers have taken this into consideration, and incorporated relays in the rail voltage circuits, of most high end amps.  or surge resistors in the less than high end.

So go ahead run your equipment 24/7  the repair shops love you!!

Properly designed electronics doesn't have components under a lot of stress.  There is a lot of industrial and commercial electronics that stays on for decades including home phones, elevator controllers, phone switchboards, cellphone towers etc. Pretty much all cellphones are on 24/7.  Failure is usually caused by external conditions (heat, mechanical stress, water condensation etc).  Test equipment, my company made in 70's, still works today after more than 4 decades of continuous operation.  

Right.  The only exception is tubes.  ARC keeps track of the time on their tubes and puts that info in the display.