I'm guessing the "sounding good out of the box, then sounding bad" has to do with you getting adjusted to the sound. It's new, you want it to sound good, so it does. Then reality hits and you actually listen to the component. Break can't have a "typical" time associated with it. A dealer I used to work with bought a pair of B&W N804's and he swore that the bass got much better after two years.
Break in period
What would the forum say about how long or how many hours of play time needs to occur before you can establish that your new loudspeakers are playing at optimum performance? I've heard opinions on this all over the scale!! Does this depend on the type and brand of loudspeaker, material of drivers, power being driven, etc? Can we agree on a nominal time period? I realize it may also depend on how loud you play them as well. Any thoughts? Many thanks.