No. I kept my Boulder 1060 powered on when I was home on the weekend & found the amp was 95+% warmed up after 2hrs (ie: good enough), otherwise I left the amp on standby. With my current Vitus SIA-025. I find myself in agreeance with Chris Thomas's comments in his Hifi+ review -
"From stand-by, straight into class A I would say that you are looking at a half hour before it really begins to sing and then it just seems to keep getting better. Even after a solid afternoon and evening's listening I would swear that the amplifier was growing more fluid, textural and resolute with better dynamic contrasts, tonal shading and the delicacy of its musical message just seems to become more profound."
To summarize, there are no hard and fast rules. The benefits of keeping a (solid state) amp switched on all or most of the time vary from amp to amp. But rule of thumb, large amps with oversize power supplies and filter banks will generally benefit more from being left on as it takes the psu's longer to warm up and reach optimal thermal conditions.