UA 3913 then UA 281 at Houston
Denver → Houston → Denver
Timetable, Houston time
21:22UA 3913 from Denver at the gate
09:40UA 281 to Denver leaves the gate
12 h 18 apart on the timetable, overnight
UA 281 leaves 12 h 18 after UA 3913 arrives on the timetable: more than half a day, so not a connection we count.