UA 2638 then DL 2709 at Houston
Chicago → Houston → Atlanta
Timetable, Houston time
13:35UA 2638 from Chicago at the gate
08:05DL 2709 to Atlanta leaves the gate
18 h 30 apart on the timetable, overnight
DL 2709 leaves 18 h 30 after UA 2638 arrives on the timetable: more than half a day, so not a connection we count.