Hi RinPoche, Richard of course is correct. If your M625 S2 is factory-fresh, you can expect it to evolve for as much of 1500 hours.
It is quite likely that during the first 500 hours or so you might experience days in which the sound is strangely anomalous... perhaps dark or univolving... These dips are short term. The overall trend is towards purity, subtlety, and resolution.
By about 800 hours, the break-in progress becomes asymptotic, with progressive tapering of sonic evolution towards completion.
Guido