Solid state amplifiers do have a warm up period in which time the bias current in the output stage stabilizes. Usually this is controlled by a thermal feedback loop, and until the heatsinks reach a stable temperature, the bias may not be optimum. In some cases, this could lead to a lean bias situation which could cause more crossover distortion than the amp would otherwise exhibit. The effect would be much more audible with extremely sensitive speakers, like my 106dB/Watt horns than speakers with medium to low efficiency.

Tube amps reach operating temperature more rapidly because of the much higher bias current flowing though the output stage in comparison to a solid state amp, and the fact that tube amps do not have heatsinks which slow the warmup process.