As a beta tester for a boutique cable manufacturer, I wouldn't listen to a cable without 24 hours of break-in. Certainly significant differences can be heard immediately. There was often a significant change of character between new and broken-in cables, mostly better but sometimes worse, emphasizing a negative change. Professional cabling less significant, especially balanced cables.
To those who claim only speakers require break-in, NO! phono cartridges (maybe other than DC Audio systems) require break-in of 20 to 100 hours to optimize the suspensions, just as in dynamic cone speakers. My numerous Dynavectors and Benz cartridges-50 hours then, wow!