The Psyllium and the Bentonite (BP) have >never< been part of the MC. The BPs shakes as they're called round these here parts can be done at any time. They don't hafta be done while on the MC. I am a firm believer in doing the Master-Cleanse neat without anything added that could interfere with it's cleansing and healing action.
The SWF (Salt-Water-Flush) should be done in the morning on an empty stomach. It's done by mixing 2 teaspoons in a quart (32 oz) of warm water. The type of salt you use makes a big difference in the taste. The best I and many here have found is Celtic Sea Salt (grey). It is much mellower and less astringent than any of the white salts.