Shavez Saifi

Learning a new foreign language is quite a task, particularly in East Asian languages such as the Japanese language. One can not precisely say how long it will take to acquire primary language skills. As you have asked, reaching ahead, many factors may affect time & duration and proficiency, such as age, cognition and learning background.
According to the JLPT standards, the student who has completed 300 hours of Japanese language learning 300 kanji and 1500 vocabularies can be said completed elementary level. Generally, it takes 5-6 months. However, new foreign language teaching methods such as TPR, audio-lingual, communicative approach, silent way etc., may help and make the learning process comparatively more effective.
In so far, JLPT N2 is concerned; it is advanced intermediate level. It may take a year and a half, depends on the learner's enthusiasm and interest. In addition, language is spoken, so you must learn not only the language but also the essence of the language, which incudes the social-cultural and linguistic aspect of the target language. I hope this may help.
Feel free to ask for any help.