Solid state preamp warm up time?

I don't know what you have for a preamp and amp but I would worry about the safety of leaving the amp on and turning the pre off and on.

Leave it on 24/7,I have owned preamps(Class'e that did not even have switch to turn off.I would not keep the power amp on 24/7 that is overkill.

Leave ANY SS device on 24/7/365, unless you know you will be away for a few days, or there's a thunderstorm on it's way. A pure class A amp will draw some juice and throw some heat when quiescent, but any other class won't be an issue. You'll notice a major sonic difference(warming up) if you turn the power amp on and off. Give it a try, both ways(same music/volume levels), and report your findings. Of course: all that depends on how resolving the system is, and how critical/discerning a listener you are.

I personally don't trust leaving any audio preamp or amp on all the time.If the company that build it says to do so,I'd still pass on the idea.Every piece of audio gear I've listened to(tube or solid state)seems to reach its full potential in a half an hour or so.I imagine you will get a lot of opinions,but for safety reasons I don't like the idea.A lot of class ab amps get fairly warm,depending on the bias and design.Pre-heating sounds like a good option. Things do fail.Just my 2 cents.