How important is it to have identical speaker cable length?

I would not fret…

But when the capacitance is # pF/meter, and inductance is @ uH.meter then the number of meters can matter.,, and the resistance is also expressed in @/meter (or per foot in freedom units).
It should make a measurable difference, which is better than a physiological difference. IMO.
But I doubt one would hear much of a difference. The room would likely have more of a difference.

Now with over 40 years of analog design, I have come to the conclusion that the more you know, the more you realize how much you don't know.

Ala… Dunning-Kruger.
There are other practitioners of DK are also present here, so no offence intended towards you @spatialking … it is a wise observation and consistent with the DK findings.