akaRadar,
kcarlile is correct. Any "break-in" needed--if you believe that the woofer's surround needs loosening up, which on the face of it is ridiculous--happens in a minute or two of your running the sub with some good bass material.
If the compliance of the surround material of a woofer were to change with use, the performance and measurements of bass output would continue to change over the life of the product. This doesn't happen (unless it's an old speaker from the '70s or '80s that used a type of foam surround that would often disintegrate over a decade or so).
As ken pointed out, "break-in" is largely a product of your ear/brain accommodating a new source of sound reproduction interactiing with, and influenced by, your particular room and the subwoofer's location in that space.
Regards,
