There is no airside connection between concourses H and D/E, so you'll have to exit the H secure area and go back thru D/E security. If you're traveling in F, or are a mid- to high-level elite w/ AA, you can save some time by using the elite security lane. Otherwise, I'd say that you'll need at least an hour to make the H --> D/E transfer. You might get lucky and do it in less time, but MIA can be a veritable zoo sometimes.