Typically the sound will change a lot... being less trebly and more natural... often takes a lot more than 100 hours.
I'm not sure why, but many companies are shy about documenting the long burn in... even through it is required. My Audio Research gear took 600 hours to stabilize and even after that there was very slight improvements over the next 400. I burned in three of the same amps... and it followed exactly the same pattern.
I’d run it 24 x 7 for a couple weeks.