The Japanese Language
Should I move to Japan to learn Japanese faster?
The general consensus of people who’ve tried this is that being in Japan offers no benefit to learning Japanese and can even be a distraction. Unless you can already conduct yourself in Japanese, you will find little benefit. See this link for a few anecdotes.
How long does it take to learn Japanese?
The US Department of State puts it at over 2200 hours of study. That’s 4 times, what they anticipate for Spanish or Swedish. See this page for more.