It depends on the design and manufacture of the speaker. A good design and well built won’t need break in. It should break in within a minute or two perhaps an hour at most.
The air suspension and voice coil motor should dominate the woofer response and not the spider or rubber surround compliance.
Tweeter motor should dominate the tweeter.
If the response drifts over hundreds of hours then the speaker response is dominated by minor factors like spider and surround compliance. It suggests a weak drive motor and a lack of air suspension relative to everything else. It suggests that the speaker will not be very linear in response. Open baffle speaker woofers are the most likely to need break in.
The air suspension and voice coil motor should dominate the woofer response and not the spider or rubber surround compliance.
Tweeter motor should dominate the tweeter.
If the response drifts over hundreds of hours then the speaker response is dominated by minor factors like spider and surround compliance. It suggests a weak drive motor and a lack of air suspension relative to everything else. It suggests that the speaker will not be very linear in response. Open baffle speaker woofers are the most likely to need break in.