I truly don't know because I've always done it this way (this is my sixth fast) but now I'm curious; maybe next time I won't do it and see what happens.

I believe it is best to do The Master Cleanse as is for at least a week, ten days is even better. Then, if you want to experiment with P&B shakes you can add them to the cleanse. By sticking to the liquid diet you give the gunk lining your colon to soften as it absorbs fluid and the lemon and cayenne loosens it, and the most recent layers of fecal material is removed. When you let the mucoid plaque, gunk or whatever name you use to describe to the old hardened mucus that lines the lower bowel of many adults, begin to soften, then the psyllium will be more likely to sweep it away and give you an effective bowel cleanse. The primary purpose of the Bentonite is to adsorb, that is to draw and hold toxins released during the cleanse. Care must be taken not to use too much as Bentonite can be constipating.
P&Bs can be used while continuing to fast or after beginning to eat healthy foods. The most important things are to add the amount of psyllium used gradually and to drink plenty of water.