UA 3913 then DL 1585 at Houston
Denver → Houston → Atlanta
Timetable, Houston time
21:22UA 3913 from Denver at the gate
10:00DL 1585 to Atlanta leaves the gate
12 h 38 apart on the timetable, overnight
DL 1585 leaves 12 h 38 after UA 3913 arrives on the timetable: more than half a day, so not a connection we count.