There are differing opinions. Some say you take them for 30 days and then take them one week per month thereafter, others say to take them 10 days on and 5 days off for three months and then do a 10 day maintenence run every 3 months thereafter, another source says to take it for 90 days, lay off 30 days and then do another 90 day run... It all depends, I supposed, on how heavily you are infested, what kind of parasites you are cleansing, how long you have had them, how fast you want to get rid of them, etc. etc.
You apparently have to view them like you would termites, roaches, ants or wasps. You exterminate them until they are all gone, and if/when they come back, you exterminate them again.
Listen to your body. It will tell you what it needs.