My experience (not with 602's) is that they change a lot after 4 days of running, basically 24 hours everyday, and can can continue to break in for many months, like 7 to 8.
Awful sound from B&W's: Break In needed?
I've bought a new pair of B&W 602 S3 and they are sounding awful with my COnsonance CD120 and Arcam A80. I think they need a lot of breaking in, or otherwise something is wrong with my system. The sound is harsh, and the midrange is shut in. Have you guys experienced something similar? Can I expect to get a really better sound from my speakers after the break in period?