I have quite a few earphones pass my way via Head pie and have found a good 50-100 hours improves on the initial sound on most of them. Some require more.
Usually the bass tightens up, treble gets smoother and sometimes the mids come up a bit.
I usually listen during the day and leave them playing over night (8-10 hours) at a moderate level to burn/break them in.
Companies recommend it, some readers think burn in is true, some dont. Burning in for 100 hours keeps...