It really, really depends on the PRINCIPLES you're following. Time is a factor, but not as big as you think. Do yourself a favor and get http://goo.gl/FPfJfW or a similar book with good reviews and follow the principles outlined there consistently.
I wouldn't recommend it. You're depriving your body of essential nutrients. Also, after about 2 wks your body holds onto your fat instead of shedding it. The thing about crash diets is that once you stop you gain the weight right back. Why not try exercise and eat healthy. This way you can lose weight and stay healthy, and learn how to keep it off.
A crash diet will probably not work for the more you lose you are likely to put it back on faster and it is not healthy it might bring about complications. Try a good diet for it will serve you well as you learn to take better care of yourself.