I have never done a Master-Cleanse but I would suggest first to eat for a few days, so you can also go to your meeting. For the flush you need bile and the bile production slows down during a MC. So eating for a few days to get your bile production going again is a good thing to do.
As I told you I never did a MC, I have only read about it. So may be you can go through the old messages and see if you find more information.