I’m about 18 months in. I study 2-4 hours a day, seven days a week. I’m now pretty far into N3 territory. I can read certain native things quite easily and can enjoy listening to certain native things while following along.
That is just my progress, to give you some numbers. ^^ Not saying what you can or cannot achieve.
Qualifiers: Never had any classes. Never had a tutor. Found my footing in grammar pretty late, because I’m really bad at it.
I’m about 300 days into BunPro, so it took me about a year to get deep into N3 grammar - I haven’t gone through all of it yet, and I’m sure I’m missing a lot of N3 vocab, so I’d fail an N3 test, I’m sure.
To do it, you’d have to work ceaselessly, very hard, and very effectively. Kanji, grammar, vocab and lots of listening all at the same time. And plenty of reading, lest you forget earlier vocab that you drilled.
If you want to go for it, go for it! I would just advise to keep your eye out for burnout, as you said. Having to slow down and not reach N2 in a year would be a shame, but burning out, dropping Japanese for who knows how long and forgetting most of it because it’s not cemented yet would be an absolute tragedy.
And mentally prepare yourself for the fact that it won’t be much fun. You can’t really do hours a day without ever taking a break while expecting to always feel genki about doing it.