Cable lengths

If you're using a cable that's so resistive or (with speakers where it can matter) so reactive that an extra 12 feet causes an audible difference in sound, my advice would be to change cables. But if you are intentionally using your cables as a tone control, then yes they have to be the same length.

The timing difference really is too small to matter. Think about it: You can also create a timing difference by moving one speaker slightly closer to you than the other. Adding an extra 12 feet of wire to one channel would have the same timing impact as moving a speaker a few millimeters. (I'm estimating here, but I'm pretty sure that's the right order of magnitude.) Now, did you use a tape measure that accurate when you placed your speakers? And what happens when you move your head? If this mattered, audio would sound very weird.

Since the signal travels at the speed of light, there shouldn't be a timing difference but it's still a good idea to keep the lengths the same.

Great response and thank you for the knowledge. While we are on this topic what cables would compliment electrostatic speakers. Clueless and some of you have pointed out electrostatic speakers may require special considerations.

Actually the propagation speed for the average cable is probably about two-thirds the speed of light.

Velocity (m/s) = Sqare root (1 / (Li*Ci)). Li = linear inductance of cable (H/m) and Ci = linear capacitance of cable (F/m).

There are no absolutely newtral cables. The active resistance plays the smallest role especially in the wires of 10AWG or thicker. The reactance will play more important role(especially inductance). If your amp is high current and can take high capacity loads than you will not experience any audiable differences.