If you're in J, you'll get the first bus.

If there's a later flight in 4 hours, I would not expect a reroute unless the next flight is full. 4 hours sounds like a lot, but when you toss in boarding time and the time to rebook you, it's closer to 3. It's going to be hard to beat that with any reroute. And if they did, it will involve a tight connection at another airport.