From what I've read if you are going to exercise but you have just eaten a meal, wait at least 2 hours. If you had something lighter, a snack perhaps, less of a wait is fine. As far as exercising before you eat, in my experience you can eat right after you exercise. I am not usually hungry until about 30 minutes after I eat, but it's probably because I like to drink a couple glasses of water after an intense workout.
If you are just doing stretching exercises that don't work up a sweat, I'd say do your exercises whenever you want. If you aren't doing something that is going to dramatically increase your heart rate, eating before or after isn't really going to hurt anything.