I say fast for as long as you can. I don't think that the amount of time you are talking about will finish the work, but if you follow it by an equal length juice fast, that my go a long way.
As we know, juice fasting isn't as good as water fasting, but it should be very beneficial to the digestive tract as most of the juice, if properly strained, is absorbed by the stomach. The rest of the digestive tract can remain inoperative for healing during juice fasting.