UA 3913 then UA 4596 at Houston
Denver → Houston → Springfield
Timetable, Houston time
21:22UA 3913 from Denver at the gate
14:25UA 4596 to Springfield leaves the gate
17 h 03 apart on the timetable, overnight
UA 4596 leaves 17 h 03 after UA 3913 arrives on the timetable: more than half a day, so not a connection we count.