Do speaker cables need a burn in period?

It's the latter.  It's only directional once you apply voltage and current.  

Now if you have a lot of time and you decide to swap ends on the cable every, say 5 minutes, while listening to music then it's no longer directional.

The wire in cables and fuses is physically asymmetrical. That’s why resistance measures slightly lower end to end one way than the other. Guess which way sounds better. 

Don't forget to burn in your connectors as well.  Sometimes it may take longer so I reuse my old connecxtors.  Also, the direction is being able to read the wire text from the amp to the speakers is correct.

Physically asymmetrical HOW?

And how can resistance measure lower at one end than the other? Stupid pseudoscience garbage. Measure a resistor with leads one way, then flip them around, and they measure the same. I’VE DONE IT. I build amplifiers.

Fuses, HAH!

NO clothes.

But then I guess many of you are laughing because I'm somewhat late to this game. Very funny.

No, I’m laughing because you’re wrong. Also because you’re late to the game. Where have you been the last 25 years? 😃