About two months of typing. If you are remotely ever interested print out a keymap of Dvorak and have it somewhere visible. Just seeing it over and over and over again will build that familiarity. Just do it today, even if you'll never end up trying it.
Without that it took me like two weeks of it actually being painful where I was closing my eyes and mentally moving each finger deliberately. After about 6 weeks I got to 30 WPM which I felt was sufficiently fast to work as a developer unimpeded. 2 years later I'm up to 60 WPM which is faster than I ever was with QWERTY. What I do is three 120 second long sessions of www.MonkeyType.com at lunch each work day.
Without that it took me like two weeks of it actually being painful where I was closing my eyes and mentally moving each finger deliberately. After about 6 weeks I got to 30 WPM which I felt was sufficiently fast to work as a developer unimpeded. 2 years later I'm up to 60 WPM which is faster than I ever was with QWERTY. What I do is three 120 second long sessions of www.MonkeyType.com at lunch each work day.