H doujin where the girl meets her future self and then proceed to have some yuri time

This really bugs me since I found the idea behind that work is fascinating, and I remember reading it a few times but I couldn't for the life of me remember what it's called.

Basically she meets her future self on the mirror (more like her reflection? is stepping outside of the mirror), and she's using this to cheat on her exam or something, finally around the final scene she's having ninesome or something with her past and future self lol.