Earlier this month I had the delightful experience of having a nearly 3-hour layover at ORD shrink to 10 minutes. Same thing happened on my last big overseas trip this past fall (but for different reasons), and the gate agent hurriedly re-booked me on a totally different routing to avoid a misconnect with my international flight. I only have enough time at MIA if everything goes smoothly, which is why I decided to reschedule. If things DO go smoothly and I do in fact land on time, I can certainly try to hike over to Terminal J at MIA and see if they'll take me as a walk-in (just like I'll probably be doing at DFW earlier that day).