Chronology · 10:50pm Dec 5th, 2013
Y'know:
The more I think about it, the more I kinda like the idea that all the episodes so far have taken place during a single year.
It makes me wonder if they could actually be arranged that way. I mean, forget the broadcast order and just go with internal evidence: for instance, is there any reason why "Apple Family Reunion" couldn't happen before "Applebuck Season"? After all, reunions are a summertime thing, and apple harvests tend to come in early and mid-fall...
Let's take that a little further. Say that our ponies like their fall foliage, so they don't hold the Running of the Leaves till the last day of the season. This would explain why the trees aren't bare in other fall-themed episodes like "Luna Eclipsed" and "Super Speedy Cider Squeezy 6000"--those episodes actually happen before "Fall Weather Friends." Maybe we could assign some of the school-based episodes to early autumn before the leaves get run, too--"Family Appreciation Day," for instance, and "Show Stoppers." "Hearth Warming's Eve" is the only purely winter episode since "Winter Wrap Up" takes place on the first day of spring, but maybe we can make "Hearts and Hooves Day" a winter episode, too, by pretending that the pegasi clear the weather especially for the celebration, a month before winter's scheduled end.
The rest of the episodes, though, we'd have to spread out during the summer and spring. Further limitations? Well, all the episodes that end with ponies other than Twilight sending in a friendship report have to come after "Lesson Zero," right? And there have to be enough episodes with Twilight's friendship reports before "The Return of Harmony" to make the pile of scrolls Spike regurgitates....
Any thoughts? 
Mike
I would then say that Return happens after nearly a whole year, with the Wedding possibly occurring before his escape. And the Crystal Empire thing happening very shortly after. It also explains why Rarity, or indeed the rest of the elements, were not recognized in Canterlot, nor did Fancy Pants recognize Rainbow's name. (Twilight is a bit harder to swallow, but I assume she was just very reclusive, so few know her on sight.)
Ever since the season 4 premiere, I've wanted to go through and try to make every episode fit into one year.
I think the biggest problem with it is that there isn't enough time. There are 65 episodes in the first three seasons. That averages out to one episode every 5.6 days. But if you take into account that there are, I believe, only about five or six episodes that take place in the fall or winter, then they are about 3 days apart during the rest of the year. And quite a few episodes take place over the course of several days, and a few even take a few weeks. (Some of the two-parters take place in one day, but it's not enough to change anything.) So it seems that, at least during the spring and summer, the episodes are practically happening back-to-back. And I have a tough time believing that.
The best explanation that I can come up with is that the Equestrian year is considerably longer than ours. And their falls and winters might be considerably shorter than their springs and summers.
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Watch the chronology of the stained glass windows. I'm reasonably sure that the season openers and endings have to go in the aired order, regardless of what comes in between, just based on what we see in the castle.
Edit: I think we see the windows in a few other episodes too. We also have to watch for continuity in things like the Cake foals, CMC relationships (they have to meet, make the CMC, make capes, then meet Babs; Owl's Well, then Sleepless for Scoots and Dash; etc.), the Gala mini-arc, Trixie, who gets to send letters to Celestia, whether or not we can go an episode without a letter, is Owlowiscious around, Luna's interactions with others, etc.
I was going to say, the season openers and closers are in a pretty strict chronology, since they all build upon each other (S4o has Discord and alicorn Twilight, hence after S2o and S3c — and S3c and S3o are after S2c because Cadence is a married princess in both).
But then I realized: aside from circumstantial evidence, there's nothing pinning down the timing of the Grand Galloping Gala.
The GGG has to be before Twilight's ascension and after her move to Ponyville, but due to the absence of all the other major players (even Luna!), we have no clues as to what else has happened in the interim. Discord's absence during Celestia's spicing up of a dull society event could be evidence he's still in stone … or could be evidence that he's out and bored, and she's trying to keep him entertained quasi-harmlessly by adding some chaos to the event and letting him giggle from the rafters. Luna's absence is simply one huge question mark, though if you stipulate that S4o is one year out, it seems reasonable that she's just not acclimated enough to high society to feel comfortable there. Unfortunately that also removes any information on whether Cadence, as a fellow princess, is obligated to attend or not, and thus any evidence of whether it's pre- or post-wedding.
Why don't we be daring and speculate that the GGG is held in early summer? (Thus placing it as the virtually penultimate pre-S4 episode, directly before the S3 closer.) The only possible issues with this are that Dash's fangirling over the Wonderbolts, and Rarity's starry-eyed glee at high society, both could potentially be at odds with their characterization after their respective achieving-the-dream episodes (Wonderbolts Academy and the one where Rarity sings "Becoming Popular"). Given enough creative effort, though, I'm sure that angle can be squared off.
Eh, I think I'm happier just assuming the story has covered about three years, and dismissing the alleged implications of Celestia's comments in the season 4 opener. She doesn't actually say it's been only a year. She just says she can finally enjoy the celebration.
Remember, Luna apparently holed up for a while after her return. This might simply be the first Summer Sun Celebration she finally participated in.
We already know extra-diegetically that a number of the episodes were aired out of production order. And we've already seen that two of them were taking place simultaneously.
Plus, there haven't been any season breaks from the ponies' POV, so even to them it's only been 65 weeks' worth of lessons, not 3 years' worth.
Oh no, this is totally melting my brain now. I'm trying to just keep the internal chronology of my own story intact as I write, and that's hard enough. I'm covering like 15 years and at least a few apocalypses, and NOT doing it in chronological order with "The Hole In The Sun" sequel. Last thing I need is to start thinking with (temporal) portals about the main series.
On the other hand, I keep waiting for someone to do a "My Little Southland Tales" story. Heads will implode if that's ever done correctly.
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The fact she did not try to upstage them is indicative that her development stuck. 
Rainbow can be explained by her being asked to hang with them in a casual setting. Academy or no, they are still her heroes, and being asked to chill with them at a high profile event is very squee worthy.
As for Rarity, well, lets assume GGG occurs as you say. That means that she has actually met Blueblood at least once before, at the ship christening. There, he had his public face on, and she didn't interact with him too much. So she doesn't realize his is actually a tosser, but by this point he knows she is an important pony, hence his agreement to accompany her. Further, she has already been to a royal wedding between a princess and Twilight's brother, so she may feel like such a thing would be possible with other royalty. And of course, she is caught up in the glamour of the party.
Reality (and hilarity) ensues.
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It does start feeling like:
One of those sliding tile puzzles, doesn't it? Pretty much trying to jam 60 episodes into six months? I keep paraphrasing the opening line from the old "DuckTales" cartoon in my head: "Life is like a hurricane here in Ponyville."
But, yeah, it's just a thought exercise. I don't think space-time--or "spime" as a friend of mine always calls it--allows for such severe condensation as squeezing all those episodes into one year would require...
Mike
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Maybe they have long years.
Or maybe things are a bit wibbly-wobbly.
Augh! Now you've gone and poked me in one of my pet peeves!
Any "one year" chronology would be a huge mess, and require massive rearranging of the episodes, tossing things from one season to other and destroying stuff like the character development that has happened along the way. Yes, there's some stuff that's shown out of order (Winter Wrap-Up and Fall Weather Friends are pretty clear examples of that, but it's easily explained by the show's schedule and their desire to have a holiday episode in S1.)
And the thing is, there is no reason to contort things like this. Celestia does not at any point say that this is the first Summer Sun Celebration since Luna's return, only that now she's actually looking forward to it because it's become a celebration of their reunion. Which makes complete sense if this is the first SSC where Luna is participating as an equal with her! Meanwhile, things in the show suggest, or are congruent with, that it's been about two-and-a-half to three years since Twilight arrived in Ponyville. Nobody argued that it was all taking place during one year until people saw the first part of the S4 premiere and misunderstood it!
...
I'm sorry. This whole thing turned into a weird hot-button issue for me. Usually, I can take various differing interpretations of the show and the characters in stride, even when I disagree. But for some reason, arguing about the timeline in this way brings out the belligerent nerd in me who refuses to give up while there is still someone wrong on the internet.
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You. The cut of your jib. I like it.
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phrases.org.uk/images/jib.jpg
Why would I cut this? And why would you like it??
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Well, you had to cut the jib of the airship to sabotage it, because otherwise it would have forced Rarity to go to another launch ceremony rather than the Gala.
… Or was I not supposed to tell anypony that was you?
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Quiet! You fool!
THEY might be listening!
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No, no:
I assure you. No one's listening. Please, do go on. <scribbles hastily in officially-labeled spy notebook and adjusts false moustache>
That Incognito Mike Guy
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In the wake of the big reveal in "Daring Don't" that Daring Do and Ahuizotl are not fictitious characters, but very real enemies, I'm wondering if Daring Do, a.k.a. "A.K. Yearling" isn't a member of the Clandestine Corp, or at least has worked with the C.C. on occasion. After all, Indiana Jones periodically found himself working for the U.S. government…
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There is definitely:
A story in that idea, isn't there?
Mike