@samac, yes all class D amps that have been in my system took over 1K hours to break-in and stabilize. But this has also been my experience with class A/B amps, with CD players, with two tube-based line stages, and with the Rowland Aeris DAC..
On the other hand, I have not tried in my system every amp on the market today, so I will not categorically state that all amps require over 1000 hours to break in...
Guido