Sound of cables breaking in?

+1 Stringreen.  That is how it happens for me.

OP, that is also what I tend to find, although it seems to vary for each product, and sometimes the break-in can be quite long, even really long, and occasionally shortish.

There is a scientific reason for cables sound better after a while that has nothing to do with "burning in" electrically but is more of a mechanical nature. When you move or coil-uncoil them the strands are moving with respect to each other and the metal in the conductors is being "stressed". It takes a while for them to "fuse together" again in their new position. This is especially true for silver-plated conductors. 

It is more "settling down" than "burning in" and you are recommended not to move your cables once they are installed. Unless it is absolutely necessary you are best off with  leaving them alone for this reason.

I'm not claiming that electrical "burn-in" and directionality of cables don't play a part as well. Only that the mechanical "leave them alone and allow them to settle in their new position for a few weeks" is more important than electrical "burning in".

Movement has a slight effect but a cable sounds different as an electrical signal passes through it.  The beginning of the signal will actually 'sound' different than the end of it.