How long is a "moon"? · 7:57pm Oct 30th, 2016
All we officially know is that a moon is an arbitrary amount of time which according to Jayson Thiessen has no Earth equivalent. But is that really true?
Granting that a mysterious time scale can be used without much fear in storytelling as there's little chance of continuity error, there is precisely one reference in MLP canon that corresponds to an Earth equivalent, and it's likely the most innocuous comment one can imagine.