Japanese JLPT level required for working in Japan

According to this website, you should have at least N2 to work in Japan.

https://www.workinjapan.com/qa/index.html#:~:text=JLPT%20N2%20is%20about%20the,still%20get%20a%20good%20position.

N2 is equivalent to B2 in Common European Framework of Reference for Languages, so upper intermediate level is the point you should aim for to work there.

http://www.sophia-cler.jp/study/ja/pdf/LevelsofJapaneseLanguageCourses.pdf

As a native speaker of Japanese, I would say that this is pretty accurate.

To reach this level, 720-1320 hours of study is needed depending on your native language and aptitude according to this: https://www.languagetesting.com/how-long-does-it-take

As someone who's specialized in educational research, you could minimize the total amount of time you might take to reach this level by taking a hands-on, active learning approach, instead of passive types of learning such as receiving lectures, solving questions on textbooks etc.

Hope the info helps!