I hear that you put back about half of the weight lost. I would think that if you do the Master-Cleanse for the full 10 days or more, you will lose more than double want you want to lose (according to your post).
This is my first cleanse ever and I am now just finishing day 6 and have lost about 12 lbs. so far. I didn't do the Master-Cleanse to lose weight but it is a nice bonus.