You can start the Oxypowder anytime, although it would probably be best to be eating solids. Start the Oxy-P on a weekend or when you can have plenty of free time to monitor the bathroom trips. Don't do like I did and get really surprised at work or in class. When you are ready to flush you can simply skip the Oxy-P for a day or two. From experience I suggest you invest in a good green food powder to keep up your mineral reserves. You can pass a lot of fluid through your colon and lose some vital electrolytes along the way. The green powder mixed in water with either a little raw apple cider vinegar or fresh lemon juice will help keep up your minerals, and keep them balanced.
Congratulations on your cleansing successes. I have enjoyed reading your posts.