Hey what are you worried about, I only have 34 minutes in Houston to change planes with Continental, but my arrival and departure is in the same Terminal "B". Continental preassigns your seat, so just go to the gate.
If your arrival and departure is with the same airline, you will not have a problem, because you will be inside the security check points, unless you try to go outside to smoke a cigarette.
Correct clear customs into Belize and again back into USA, remember stay behind the line on the floor. LOL