Warm-up time for amps and preamps

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.

There is absolutely no reason why running without input signal would be bad for any class D amp.  This strange advice was given by NuForce technician?  Are they still in business?

I believe the above rests on a misconception; it is advised by NuForce not to turn on their switching amps without speaker load - that is, with the speakers disconnected. I imagine that's what's referred to?

SS gear sounds best when the unit is left on. This is the truth to my ears based on my experience with numerous amps over numerous years. Class D amps most especially. 

Thank you, phusis!