UA 3902 then AA 2551 at Houston
Toronto → Houston → Dallas-Fort Worth
Timetable, Houston time
08:27UA 3902 from Toronto at the gate
06:00AA 2551 to Dallas-Fort Worth leaves the gate
21 h 33 apart on the timetable, overnight
AA 2551 leaves 21 h 33 after UA 3902 arrives on the timetable: more than half a day, so not a connection we count.