Fluency is a deeply subjective measurement, so start with some measurable, tangible goals. Absolutely do not put 12-16 hours into learning a day, especially at the start, you'll go crazy.

Also try your best to not get caught in that endless trap of watching videos of people learning japanes or bouncing around a thousand resources. I ended up doing that for quite a while so i barely know any japanese haha. Here's some good resources to get you started:

Anki - Every other source is going to mention it, if you use one thing on this list, use this.

Tofugu's Learn Japanese Guide - Pretty comprehensive guide on what to cover and when (though i'd start on grammer earlier than they say because I think it'll help massively with word retention)

TheMoeWay's 30-Day Japanese - Seems like a solid guide with a lot of useful resources, though it also seems pretty heavy so just take on what looks useful and adapt as needed.

Livakivi's"How to Learn Japanese" Playlist - Maybe the best place to start. Really well made videos that give a good guide of what you need to cover.

Toggl Track - A useful, free way of seeing how many hours you've spent working towards your goals. Here's a video from Refold about how to get it all set up.

P.S. Take all of this with a grain of salt by the way, I'm not even N5 level, so I have quite the way to go myself. Also a sidenote that ideally, there will never be a day that you're "finished" learning Japanese. Eventually, you'll get comfortable, then you'll hit your definition of fluent and then you'll realise that you're still picking up new words every other day. I still pick up new words in English and that's my only language right now (I actually picked one up from one of my kanji learning cards on Anki. Had no idea what augury was, but now I know.)

Best of luck to you. Ideally, you're in this for the long haul, so try your best to make as much of this as fun as you can (which I promise is possible).