I recently read a review of language-learning apps for my tablet, but it warned that it takes 500–4400 hours to become fluent. With my atrophied brain, I would be on the high end of that range, so devoting 8 hours/day to the task would take me 550 days, or about a year and a half even at that intense level.
The apps have some cleaver features. Some pop up throughout the day with vocabulary reminders. One allows you to speak with a native, but not in real time, so you can think before replying. Another narrows the new language to a specific topic (pop culture, sports, music, art, etc.).
But they are all too long for me. I have yet to master English.