Apart from the fact that "learning Japanese" in my definition already starts with the first word or character learned, I can give you a short statistic on how much time I invested before going to Japan an being able to live, communicate and work there for more than a year:

I spent:

• 3 years
• learning literally everyday for around 3 hours
• which makes 3 * 365 * 3 hours which is roughly 3300 HOURS

I used a spaced repetition software called ANKI. And I spent the first 3 months just learning the 2000 most used Kanji (Chinese characters). Only then did I start really learning words and sentences.