Hi raddish, actually a colonic right now, or during the next few days, would be excellent. If you hadn't already started your fast I would have recommended it a few days beforehand.
Then, with a daily enema afterwards, you'd be starting the fast with your colon already in a healthier elimination and detoxing mode. But anytime from now on that you decide to have it will be great.
Usually there is no discomfort from a colonic, and most people find it more comfortable than an enema. The only time people tend to have cramping and discomfort is when their colon is impacted with stool. If you have been fasting, and haven't been constipated in the past, you will probably find it not to be an uncomfortable procedure.
I also encourage you to consider taking a saline solution enema every day for the remainder of your fast. See the following links for more information: