Honestly for three days I wouldn't do it because you get a completely distorted picture of the Master-Cleanse - those are the three days most people feel lousy. If, of course, you do not take caffeine each day and have a fairly clean diet you should be okay. My first three days are always tiresome due to hunger pangs but I don't have the whole headache and withdrawal symptom thing going on.
You could always start out with the intention of going three days and if it works out for you, you continue?