When does true ending begin to differ?

Posted on here a few days ago about missing the third semester by not spending enough time with Maruki. Anyway, I decided to finish the game and do a NG+ to get the true ending. I’m around 20 hours in and just finished Okumura’s palace. I’ve been skipping through all the cut scenes and dialogue (aside from confidante stuff I missed on my first save) and I was wondering at what point should I stop skipping the dialogue and actually start paying attention? Is it after clearing mementos and beating the holy grail that the game actually starts to differ or is it before that point?

Link to original post: https://www.reddit.com/r/Persona5/s/488aHzbHfH