Series of chronological events which MUST be directly sequential:
1. FIRST Summer Sun celebration seen, NMM's return. Twi is wingless.
2. First Winter Wrap Up. Twi is wingless.
?: Hearth's Warming Eve (uncertain temporal placement)
3. Dash acquires Tank. Twi is wingless.
4. Canterlot Wedding occurs
5. Crystal Empire Returns (assume at least several weeks have passed)
6. Equestria Games announced (at least a month passes) Crystal Empire chosen.
7. Twilicorn cometh! (more time passes)
8. Training for games (several more months)
9. SECOND Summer Sun celebration happens in Canterlot, AFTER TIREK. Twi has wings. Tree castle is created.
10. Tank's for the Memories must come after #9.
The problem arises here. If we are expected to assume all of the show has taken place in less than a year and Dash got Tank in early spring, this means everything that has taken place since Dash got Tank has occurred in less than 8 months. This means some of Season 2, and all of seasons 3 and 4, plus the first two episodes of Season 5 (including travel time to and from Equal Town back to Ponyville) since Twilight was still acclimating to the castle.
There simply isn't enough time, meaning Tank must have passed one winter already, and the sole way this could have happened would be to set this episode back in Season 3, BUT that cannot be the case because of the castle!
Therefore, TFtM stands out rather awkwardly in the timeline as it MUST occur, and works far better as an story which would have fit neatly in Season 2 while Dash was still fairly self-centered and short-sighted, being set just before Hearth's Warming Eve episode.
If I watch TFtM while mentally removing the castle and Twilight's wings, Dash is perfectly in character with her Season 2 self.