Break-in is definitely a must if you're buying new. Do the experiment yourself and listen to whatever reference you use at different times. Some of the changes on some cables can dramatic and pretty unsavory like "what the f*** did I spend my money on?!" Many builders will tell you how long they think it will take for a cable to get most of the way to sounding its best - I imagine that's what they'd want you to hear.
100 hours seems to be plenty for most. I've heard less and more. More definitely gets to be a drag. I've had cables that took that long and longer and it's no fun to burn up my tubes 24/7 - and hooking them up to the fridge seems like a bad idea somehow - but it's always been worth hearing what the builder intended. The cables I've been most enamored of have been mostly from more boutique builders who can tell you....some do want you to listen and tell for yourself, though. Buying used eliminates all of that though and a day of letting them settle in is plenty....this is my experience anyway.
I'm admittedly a pretty nervous audiophile who'll set up a few sets of IC's on my integrated and switch back and forth to replay a few of my reference songs back to back with different cables...really doesn't let me have any real insight, though. Impulse control isn't always my long suit....
The Dynamic Design cabling I have took three days. Much more open after 2 days and haven't changed much after 100. The changes are what makes them the only cable I've ever considered using as a loom. They became more 3D, nuanced and extended. I'm using PC's and IC's now and am awestruck by the music coming out of my system....that wasn't the case right away, began to become clear after 80 hours or so with PC's alone and after adding IC's (and being a little patient), the experience of interiorly illuminated and nuanced detail on a huge, layered, dead quiet stage with round 3D images is phenomenal. Even handed, extended with a natural control and timbre there's no etch or fatigue from my system at all...
So, patience. Siltech is a great cable and does take some breaking in - I used them back int the G4 era with Plinius gear when Plinius used it as hook up wire. Do yourself a favor snd get yourself a set of DD to listen to - you can usually get a demo period directly from them.