FYI - managed to snag 19D/F for myself and wife for IAH-MAN next week at 96 hours out. I couldn't pick the seat on the map but a quick chat session and the agent switched us no problem. My guess is that most will log in to their reservation and see that it says you can only make changes within 48 hours of the flight and give up. Appreciate the inside tip that I picked up here about some flights allowing the 96 hour window.