Yes, it's true. Not what any of us saw coming, especially coming from the grandmother of the Element of Honesty, but it is true. Granny Smith is a filthy freaking liar. I didn't want to believe it, but the evidence is there. It's always been there, right under our collective noses. And it was placed there by the writers, as if to mock our shortsightedness, to make fun of our community's need to analyze everything. All those review shows, and no one ever noticed this simple fact. Where's your god now, Tommy Oliver?
But now the shroud has been lifted, the Wizard has been revealed as a phony, there never was a Santa Claus, Bruce Willis was dead the whole time, the parrot has swung down the curtain and joined the choir invisible, the truth has been revealed.
And what was the clue that led to this discovery, the key to the writer's ultimate masterpiece of revelation and cunning? It's simple, Greg: since it is now official that "a moon" is roughly equal to one month's worth of time, Granny's comment that it's been 100 moons since the last Apple family reunion in "Apple Family Reunion" means a little over 8 years passed between Twilight's arrival in Ponyville and "Apple Family Reunion."
There are a few explanations for this, but only one is feasible.
1.) The writers don't are, which is obvi not true, emmiright?
2.) Equestria time is different than Earth time, which is a dumb argument. If that's what Meghan McCarthay meant, she would have said that.
3.) This statement is true and ponies just age really slow, which removes some of the mystique and wonder from a 1,000 year old being, doesn't it?
4.) Granny Smith is going senile. Realistic, but 2 real for me, bro.
5.) Granny Smith is a filthy liar. I'm much more comfortable with her being full of shit than going senile, so I choose to believe this reality and any argument to the contrary will be met with violence and hatred.
Of course, it can not only be assumed that Granny Smith lying about this means she lies about everything else, including who really murdered the Apple parents, but that she is omnipotent. Think about it: who was that lie for? She ain't fooling the Apple siblings or anypony else, so she's lying just to annoy the audience with the lack of a consistent time frame. She broke the fourth wall just to torment us, and who knows what else she's capable of when angered.
So watch out, mate.