There is a secret in this update but it's very specific to get and so far no one has found it yet, or at least comunicated about it
Viewing post in Version 0.67 (Haruki) - Public Release comments
just a guess, but i think it means that the day 17 has something to do with getting the secret on day 18 or 19 . it would be not the first time in the game that for a special thing to happen you need to do something days before.
the annoying thing for me is, since i dont know WHAT the secret is, i wont be able to tell if i got it or not XD
the secret is a bug a tester triggered that turned Haruki naked. People liked it and Basket decided to keep the bug in the game, turning it into a secre, however, we don't know how to trigger the bug and Bask said it's a very specific process.
https://twitter.com/BaskyCase/status/1762938161968115822