Day 8 Lightning Returns - How Much Time Left After (SPOILER)

Hey y'all. Been playing through Lightning Returns for the first time and I've been having a fun time with it. It kinda feels like if Shenmue and Majora's Mask had a baby. I'm nearing the end of Day 8 and I have "3 Days Left". I got through three of the four main bosses pretty easily, but >!Caius!< has been melting my face so I'm going back and grinding a ton of side quests out to level up and get good equipment/abilities. I think I might have a new equipment setup, but I don't want to waste my time going all the way back to him yet.

Without story spoilers, I have a very vague understanding that once you complete all four bosses, >!you get "The Final Day" which sounds like its on its own schedule. Does that mean that I can spend three days grinding out as many sidequests as possible and then pop Caius with an hour left on the clock and still be good for the endgame, or should I try and get him done ASAP because I still need that time leftover for anything that comes next?!<

I think I'm on the right track, but I just wanna make sure that I don't accidentally blow the past 20-something hours of my life.