The instructions should read TWO heaping teaspoons, five or six times daily.
Yes, it is a good idea to cleanse longer than a week; we have used IF#2 for many cleanses (and in general to soothe the intestinal tract and suck up other toxins while doing other cleanses), and we always have the best bowel cleansing results when into the second week.
When checking out the Dr. Schulze link at the top of the page, I see that the instruction now say one heaping teaspoon...but they've said two heaping teaspoons for decades.