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> they once swapped out a cable that was a few feet longer than the older cable and that's why the latency increased

That was not why. Possibly the cable made a difference (had an open circuit that made the NICs back down to a lower speed; noisy leading to retransmissions) but it wasn't the length per se.

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It can be the length, there's about 1ns latency per foot.

Well, it depends on the granularity of the time scale right? When you're measuring milliseconds, then the cable length probably isn't a thing factoring into your latency calculation.

When we're measuring time on the scale of nanoseconds then, yes, cable length is definitely something we care about and will reliably show up in measurements. In some situations, we not only care about the cable length, but also its temperature.

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