UA 3913 then UA 564 at Houston
Denver → Houston → Calgary
Timetable, Houston time
21:22UA 3913 from Denver at the gate
09:33UA 564 to Calgary leaves the gate
12 h 11 apart on the timetable, overnight
UA 564 leaves 12 h 11 after UA 3913 arrives on the timetable: more than half a day, so not a connection we count.