UA 3913 then AA 4778 at Houston
Denver → Houston → Philadelphia
Timetable, Houston time
21:22UA 3913 from Denver at the gate
14:25AA 4778 to Philadelphia leaves the gate
17 h 03 apart on the timetable, overnight
AA 4778 leaves 17 h 03 after UA 3913 arrives on the timetable: more than half a day, so not a connection we count.