My Little Pony LVI:S Has Left the Playground!

[Eakin]

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I prefer to think that her immortality has warped her ability to sense the flow of time as a normal pony does. While she has a daily routine, after a few years time just seems to blend.

NMM? Thousand years
Crystal Ponies? Thousand Years
Discord? Wait that was before NMM... Two thousand years!
That time she and the griffin ambassador got really drunk on cider and she can't remember all of that night? Thousand years.

I'm taking this one step further and making it my new head-canon: One Thousand Years is literally the only interval of time Celestia understands.

C: My faithful student, your next lesson in magic will take place in ONE THOUSAND YEARS!
T: So, same time next Thursday?
C:...Yes