Be sure and take some lemonade with you so you can "power up" if you find yourself overly fatigued. If you can, get a small bottle and take a little Maple syrup with you so you can get some quick energy if you need it.
Even with the same individual cleansing can vary in degrees of intensity. I would say to do the best you can, but be prepared to cut back if the need arises. Never do anything to put yourself in danger. It would be great if you had someone to run or walk with you. You will probably be able to sense if you go into a period of deep detox. If or when this happens, rest and do not force yourself. Listen to your body, that may sound trite, but it is the only reliable answer, there are just too many variables to give a cut and dried answer.