I asked Jeffrey Smith about break-in, and he said that he hasn't experienced and did not expect any improvements with break-in; however, he did say that some customers did experience positive effects. I have had one pair (just received a second pair for biwiring) for about 3 weeks and don't think I've heard any changes.
I must say that these are the best cables I've ever used and by a considerable margin. Highly recommend trying them...you can return them within 30 days for a refund if you don't like them.