This is right on - I speak from personal experience here. I made the huge mistake of trying to do a second Master-Cleanse only 3 weeks after my first one of 21 days! It wreaked havok on my body and mind!
Slow and steady wins the race ... it helps me to remember that I didn't get loaded with toxins overnight, and they aren't now going to come out overnight! A 21-day Master-Cleanse is an awesome accomplishment, and you have done wonders for your body already! Pepe's advice is sound - I would take it if I were you! :^)