UA 3913 then UA 2124 at Houston
Denver → Houston → Chicago
Timetable, Houston time
21:22UA 3913 from Denver at the gate
09:37UA 2124 to Chicago leaves the gate
12 h 15 apart on the timetable, overnight
UA 2124 leaves 12 h 15 after UA 3913 arrives on the timetable: more than half a day, so not a connection we count.