I feel I can exercise best at least two hours after a meal and ideally three. It feels like vigorous exercise is interfering with my digestion if it's too close to a big meal. I don't have as much energy to workout as I'd like to before breakfast.
One thing I love to do close to after a meal though is take a long walk. This works especially well when the only time I have to exercise that day is right after eating. And while it's not convenient for me to do this now, I've enjoyed a brief walk before breakfast at times as well.
I walk to work and walk home and walk to any errands which adds up to 9-14 miles per day and it is usually after I eat.
It varies... Sometimes I only have time to exercise after I eat. It's important for me to have my daily movement, so I don't care if it's right after my meal. Ideally though, I wait about an hour or more. It also depends on the type of activity I'm doing. Lately I've been hooked on the elliptical machine, so use that one for about 30-45 minutes of vigorous training. But other times it's yoga or strength training. I've noticed that I don't have a problem doing those after a meal, whereas the cardio seems to make my stomach upset if I train too hard right after eating...