He's living in Japan but has never actually been there.
Amazing.
Anyway, I've been planning to take the JLPT Level 4 test this year to increase my chances of getting into BA Japanese Linguistics next August.
Is it worth it?
How long do you think it would take me to study for Level 3?
It depends on how well-rounded your studies are. Last spring/summer, just over a year ago, I began studying Japanese for the first time. I began with Hiragana and Katakana, and a Barron's grammar book which was written entirely in Romaji but offered a decent discussion on the basics of Japanese grammar. Along with 2 hours a week of free classes at my local ward center (I was living in Japan at the time) I gradually built up a decent vocabulary and understanding of some of the grammatical basics. I wasn't reading any Kanji or speaking much but I was able to fumble through some stuff.
Lately I've been doing a lot of language exchange, and my speaking skills have increased steadily, however it wasn't until a few weeks ago that i found a good teacher and really began knuckling down on my kanji (finally). At this point in time I'm confident I possess the tools to pass the JLPT4 rather handsomely and back that up in conversation too.
So like I pointed out to the OP, it's definitely possible to, within a couple of years, bring yourself to the point of being able to pass a level 3 test. But remember the JLPT itself is not a clear benchmark on overall Japanese communicative ability, it is moreso a standardized test of your knowledge of the written Japanese language with some listening comprehension. Turning that into everyday conversation, intuition, culturally relevant comprehension and so on will be dictated by how much of your bulk learning is put into action in an immersive environment.
So basicaly I've just repated what I said in my other post haha but yeah, within a year I think you'll definitely be able to pass the test. Again, depending on your immediate goals, if you want to be able to USE everything you learn I suggest joining a Japanese language exchange circle or something, hanging out with exchange students, etc. That way alot of what you learn will be more than just theory and fact, it will be your own language. Why simply memorize a word's meaning, when instead you can know it immediately when you hear/read it because you use it every day.