The time in which you develop a tolerance, and the degree to which you can tolerate it, and the time in which in takes you to reset your tolerance all vary much from person to person.
When you feel like the amount you take daily is no longer affecting you, or not affecting you as much as it once did, you can take some time off. Maybe starting at a week, and then start taking it again and test if your tolerance has decreased or reset completely.
If you take a week off and you still don't feel much affect from the amount you normally take, take more time off, or ramp up your intake.
Essentially, just go off of the feel.