I recommend separating the 'Purge Drink' from meals and nutritional supplements by two hours if possible. Two hours on either side of eating is ideal.
If you have to shorten the separation it's better to do this prior to eating than to drink the purge too soon after. It's acceptable to drink it it as little as one and a half hours before eating.
Scrubbing the colon with a clean brush
The purge components are designed to both scrub and soak up waste material from the sides of the colon. The biochemical and somewhat magnetic make up of the drink, along with it's texture, can do the required cleansing "work" most effectively when the drink is exposed to the intestinal walls rather than being mixed in with food. If you eat too close to the purge, it's kind of like trying to clean with a dirty scrub brush and sponge... you'll still get the job done but it won't leave things as clean and it will take a bit longer to do.
Don't soak up dietary nutrients
There is an additional important reason to separate the purge drink from your food. When taking a fibre supplement or eating a lot of fibre in your diet regularly it is important to time the consumption of it two hours away from your meals, so that the fibre does not interfere with the optimum absorption of the nutrients in your food.
It is even more important to separate the purge drink from your medications and vitamin/mineral supplements, for the same reason.