Everyone is different. I find that the orange juice sets off my digestion and I get VERY hungry quickly, so the longest I've lasted drinking just orange juice is 3/4 of a day. Other people have had a different reaction and find the orange juice very satisfying and can go for the recommended two days.

Good luck! I bet you will find that the orange juice is the best thing you've ever tasted! One tip - do NOT drink frozen, pasteurized orange juice - only drink freshly squeezed. I had some Tropicana last time and it almost made me sick - I could literally taste all the chemicals and crap used in processing it.