This got picked up on Twitter, but apparently one guy took the dates and occurrences that happened in the Sealing Club CD stories.
・蓮台野夜行は11月3日
- Ghostly Field Club takes place on November 3rd
・蓮台野の2時30分に盤面の月が見える
- The surface of the moon is visible at 2:30 am on that day
・大空魔術の日は満月
- There is a full moon on the day that Magical Astronomy takes place
・大空の日、日の入前に宵の明星が見えるほど金星が明るい
- On that day, Venus is bright enough to be seen before the sun sets
・大空は卯酉東海道を挟んで蓮台野の翌々年
- MA takes place two years after GFC, with Retrospective in between
これらを満たすのは
蓮台野夜行 2151年11月3日
大空魔術 2153年1月10日のみ
The only real-life dates that correspond to this sequence of events are:
GFC - November 3rd, 2151
MA - January 10th, 2153
The reasoning being that this is that in MA, Renko says "At 16:31, I saw the evening star." (AKA Venus), and that the sun sets at the earliest point in Kyoto around December through January, which is about 4:50 pm. This also coincides with the period when Venus is bright enough to be visible to the naked eye.
And then, he followed up with a summary:
2151年11月3日 蓮台野夜行の墓回し
2151年12月 「博麗神社を見に行かない?(紅葉の終わり頃」
2152年9月20日頃 卯酉東海道(※秋の彼岸の場合)
2153年1月10日 大空魔術
2153年8月以降 月面ツアーの予定時期(夏休み以降なので
November 3rd, 2151 - Events at Rendaino
December 2151 - Renko suggests going to the Hakurei Shrine at the end of GFC
September 20th, 2152 - Riding the Boyo Tokaido Line (sometime during the Autumn Equinox)
January 10th, 2153 - Magical Astronomy
August 2513 or later - Scheduled visit to the moon (since it's after summer vacation)
Considering how ZUN has been trying to line up events in the game with real-world times (even as recent as ULiL where Kasen mentions lifting a 130-year ban that coincides with the formation of the Hakurei Barrier), this theory seems quite plausible. It would also give time for Sumireko to have descendants (that somehow still bear her family name) and for Tokyo to recede enough that Kyoto becomes the capital again.