Driver breakin period, what’s the science?

Very, very,very little difference 

Almost all the break-in occurs, at reasonably loud volume, in the first 5-10 minutes. If you still hate them after that period of time, then you hate them, though keeping them will cause your brain to change far more than the speakers.

However, changes in mechanical compliance of the structure can keep occurring for 5-10 hours. After 10 hours, not much.

The changes are measurable.  As the suspension breaks in, you can measure a difference in QMS and typically a bit In FS and QTS.  The biggest difference in sound definitely occurs in the first 45 minutes of played at a decent volume. (I'm not one to recommend real cranking), but I can tell you that the nuances of a speaker continue to change for at least a couple hundred hours.  

significant difference

components in the crossovers, driver surrounds esp mids and bass

the better the speaker and the more resolving the system is, the more this can be noticed, happens over the first 100 hrs at least... for mine, changes were noticeable up for 300-400 hrs...

this is significant... those who say no just don’t know...