How important is it to have identical speaker cable length?

To the speaker, no, a small difference is not a big deal.  But holmz is right, the additional pFd and uH could make a difference to your amplifier.  Remember, the output is also the input due to the feedback network.  As long as your cables are low in inductance and not too high in capacitance, you should be okay.   On the other hand, I have had good amplifiers tendency to oscillate when the capacitance in the cable is too high..

This depends on the wire gauge of your zip cord ;-)

Many audioholic myths are debunked on this YouTube channel ... this video is on speaker cable length:  https://youtu.be/WXPAjnmhK_g

This forum…..first answer:  absolutely no problem.   Second answer: oh my god no. Third answer: perhaps yes perhaps no.  Unbelievable. 

I personally cannot stand the Audiohaulics guy.  His videos are unwatchable to me.  But if you trust him…..