I believe the best break in strategy is to play at moderate levels for the first 60 hours, but don't push the speaker to it's limits during this period. Kind of like breaking in an engine.
For those of us who can hear "speaker break in", depending on the speaker, it seems to be at around 50 to 80 hours. For those who can't hear the difference, it occurs within the first few seconds. A speaker is an electromechanical mechanisim. There are some barely measurable changes that take place during the initial use while surrounds and other mechanical components adjust to use. Since the changes appear extremely marginal, many believe you can't hear the difference.
Nothing to argue over, if you don't believe anyone hears a difference, then there is no such thing, & our ears just became accustomed to the sound.