Easily less than two years of self study.

-Learn hiragana and katakana from realkana or use mnemonics. Takes 1-2 weeks.
-Read through Tae Kim's Grammar Guide multiple times.
-Learn vocabulary using Anki and download the voiced Core series decks in order to get started.
-If you keep having trouble distinguishing kanji try Heisig's RTK1 and the equivalent Anki deck.

Then you just start playing easy to understand games and visual novels. If you're on PC use ITH and Translator Aggregator. Don't actually use the shitty machine translators, but get the Rikaichan or JParser add-ons. They show kanji readings and also meanings when you hover your mouse over the word. You can also use the Anki add-on Yomichan to copy paste the ITH hooked text and make your own cards. That way you learn exactly what you need in order to understand the games that you're playing. Just keep in mind not to keep JParser or Rikaichan as a crutch. Always try to read from the game window first.