It takes as long as it takes you to learn how to identify how you're misusing your eyes and stop doing it as a matter of habit. If you're open-minded, humble, adapt to new ways of doing things, learn well on your own, and can listen to your body, you may find yourself seeing clearly more often immediately, in just days or weeks, and even notice changes in your vision in a matter of minutes or hours. This is true even if your condition is long-standing. If you lack all of these qualities, you may not ever make any progress at all. Others take months or years to recover their vision as they remain only partly committed and remain distracted by life. Be prepared to dedicate at least half an hour per day of practice, preferably with the feedback assistance of an eye chart at least some of the time, and the rest of the day you should apply what you learned during the practice time.
Webmaster of http://www.iblindness.org
"I conceive that the great part of the miseries of mankind are brought upon them by false estimates they have made of the value of things." - Benjamin Franklin