It varies from one individual pod to another, but from the time you first see them, expect them to begin doing the color change in at least 2-3 weeks, give or take. I remember getting really anxious for the color to start changing on my De Arbols after the pods stopped growing.
Fair warning though, don't freak out if it's been a month and they still haven't changed color. One of my pods took over a month to fully ripen.