Okay, lets assume this. MLP is set with a different sun, moon, and possibly yearly basis. No month's are mentioned, yet days(monday, tuesday) are mentioned. So, maybe we can assume their are 100 days in a year BUT then that would mean that the apple reuinion is coincidentally on the same day as the rising of the summer sun celebration (S1 E1, Elements of Harmony Pt1), which is just too likely to happen, BUT we have also got to concider the Grand Galloping Gala. In S2 E9 'Sweet and Elite' Twilight mentions that the GGG is coming close, even though it's presumed to be a yearly thing, like most formal events are. Considering the GGG was in S1 E26 'Best Night Ever' we can assume that years are most probably closer together. HOWEVER the CMC members have appeared not to age, otherwise they'd most likely have their cutie marks. In S4 E1 'Princess Twilight Sparkle', It's revealed by Celestia it has been EXACTLY ONE YEAR since the first episode, where the last raising of the sun took place. This would mean that Twilight has only been in Ponyville for 1 year! With this evidence, we can now presume that the episodes are not in chronological order, and take place and different times then shown. Most likely would explain alot of things, like why winter last one week (S1 E11 'Winter Wrap Up), we can now say that if we put S2 E11 'Heath's Warming Eve' before 'Winter Wrap Up' it would make more sense. And we can also assume 'Sweet and Elite' goes somewhere before 'Best Night Ever'. We can also assume that since Season 1 Episodes were reveled to take place every tuesday, then we can say, without putting in the theory of episode order, that S1 took place in 182 days. Now, putting in the theory of episode order into place, we can now say thing like 'take away this episode and add these episodes' BUT we must remember that every episode of Season 1, 2 and 3 INCLUDING Equestria Girls, takes place in only ONE YEAR!!!!! so, by this theory, I can say that when Granny Smith said '100 moons' She meant '100 days and nights' UNLESS!!!!! *yes, there is more* we take into account Twilight Sparkle NEVER appeared in the episode whatsoever(S3 E8, Apple Family Reunion). If we put my theory of episodes not being in the right order, then maybe, JUST MAYBE, we can say that this episode takes place AFTER or DURING S4. But thats really just pushing it