Solid State amps shouldn't need nearly any warmup. Maybe a few seconds max depending how the gear turns on.
On good equipment a running in period is always clearly noticeable. It's just like the warm up of a car from cold.
I once had a customer who felt I was talking nonsense when I told him his amp was a bit bright because it needed warming up 1st. There was nothing I could fix in it to get it to stop doing that. So he sent it to the manufacturer instead for a better opinion. They gave him a new one, and that was no different.