When you're using activated charcoal to whiten your teeth it's recommended to brush your teeth with the activated charcoal once per day for 3 to 5 days.
Brushing your teeth with the activated charcoal once per day for 3 days is usually enough for lightly stained teeth but for darker stained teeth 5 or even 6 days per week may be needed to fully whiten your teeth using the activated charcoal.