The biggest hindrance to worldbuilding in the setting of MLP:FiM is, in my opinion, the passage of time. Or lack thereof. I was going to do this as one big post, but it hit 10,000 characters and I figured that's too ridiculous. So I've split it in two.

There’s at least three different points where the passage of time is important to the setting while having strange issues that conflict with themselves. Let’s tackle the two smaller issues first to get them out of the way.

Exactly how long is a ‘moon’? It’s a temporal measurement used a couple of times that give the impression of being an exact measurement.

First off, the shortest cycle it could refer to is the raising and lowering of the moon, so a day. I can almost see that as a strange tribute to Luna, but very unlikely.

Next is a week, believe it or not. The span between one Monday (which is derived from ‘Moon’s Day’) to the next. This one is a possibility but as Rainbow Dash actually uses the term ‘weeks’ when referring to her time away at the Wonderbolt Academy I’m doubtful that they have two terms for the same period of time.

Finally we have the ‘Month’ which is in fact another word for Moon in real life. This one’s the most likely of the bunch just due to that. Just for your information, in real life there are several types of month. Sidereal, Tropical, Anomalistic, Draconitic (I need to do more research on this one, just because of it's name), Synodic, and the one everyone knows, the semi-arbitrary Calendar month that the Roman Emperors had so much fun with (Originally the Roman calendar had 10 months, and a weird 51 day period during the winter that wasn't in any month because it was when the 'year was dead'. As I said, weird.) Out of this mess, the best one to deal with is the Synodic month, which is the time between one full moon and another. On Earth, this is about 29.53 days. (As a note, ‘about’ is used here because there the Moon’s orbit does have eccentricities due to it orbiting a body that is also in motion at an angle to said motion.) There is a problem with this, as Luna (and Celestia, and the Unicorn tribe as a whole at different times), control the cycles of the moon in Equestria. That means this isn’t really a fixed time frame, but a ‘suggestion’. Let’s just assume Luna et al keep to the same cycle time as Earth, just for our convenience. There's no proof of this whatsoever, but if it isn't a regular cycle, how can you tell time by it?

In any case we’ve got two potential timeframes, and two instances of the moon being used to keep time in the show. One in Apple Family Reunion, and other the Equestria Girls movie. There may have been mention of it outside of that, but I can’t recall.

In Apple Family Reunion, Granny Smith states that it’s been 100 moons since the last reunion. Taken literally, this means it’s been 700 days if a moon=week (a little less than 2 years), or 2,953 days if a moon=month (a little over 8 years) since the last one. 8 years is very reasonable for the gravity the characters treat the time span, but there’s a problem: Apple Bloom was present at the last Apple Family Reunion, as it was taking place in the first episode of Season 1, and she has not aged much since then. For a filly 8 years is going to make a big difference. If she’s 12 now, she was 4 then. If she was 8 then, she’s 16 now. That’s just not adding up. However, the less likely moon=week is very interesting there, as it isn’t that far off of the actual difference in broadcast dates (10 October, 2010 to 22 December, 2012, or 804 days) between the two episodes with Apple Family Reunions in them.

Then we come to Equestria Girls, where 30 moons is used, which is either 210 days (a bit over half a year), or 886 days (not quite two and half years). There is a major problem with a moon=week here. At the beginning of the movie the princesses give the impression that between portal ‘openings’ is a serious length of time that it’s critical to avoid missing. But if it’s six months… yeah, that’s very inconvenient, and sad to be away from your friends for that long and all that, but it’s not exactly life-threatening. Two and a half years however, that’s a bit more meaningful.

It’s a pity that the writers didn’t use the same ‘100 moons’ here as previous, as that would make a third explanation a lot easier to accept. It’s an idiom, a turn of phrase meaning a ‘long time’ without a precise meaning. But ’30 moons’ feels oddly specific, a little less than a third of a long time? What?

So we have two likely candidates, that each fit one of the two scenarios. *sigh* I personally prefer the moon=month one, because of linguistics, but that means having to write off the reunion in the first episode of the series as somehow ‘not counting’ as far as Granny Smith is concerned.

Let’s move on, but not too far. We’ve still got a problem with Granny Smith herself.

How old is Granny Smith, anyway? She was a young mare (not a filly as such, as she gives the impression of being older than Apple Bloom, but younger than Applejack in the flashback to when she was in Canterlot with her parents) when Ponyville was founded according to Family Appreciation Day. Yet Twilight specifically said that Winter Wrap Up in Ponyville has been happening for ‘hundreds of years’. So Granny Smith is hundreds of years old plus a bit? Maybe Twilight is exaggerating (not atypical for her to be honest,) or actually referring to the Winter Wrap Up celebration for Earth Ponies in general, and not specifically Ponyville.

Otherwise, maybe that bit previously about Apple Bloom not aging enough in 8 years was a bad assumption. If that’s true, then either their years are a lot shorter than ours or pony lifespans are at least three times what our modern human lifespans are, if not more. In either case that means that Celestia’s rule of one thousand years, while impressive, is more like 300-400 years relative to humans. I’ll come back to this one later, as it leads right into the biggest issue with time in this series.

How much can... no, that's too weak... should happen in a thousand years?