Talk:Shadow Play - Part 2/@comment-1031724-20180515201251/@comment-36700661-20180911192215

"Longest day of the thousandth year" refers to the thousandth year of the Summer Sun Celebration, in fact Twilight said it was the thousandth year of the Summer Sun Celebration in the script, and the Summer Sun Celebration is the celebration of the day Celestia defeated Nightmare Moon. It's been exactly one thousand years from then to the first episode.