UA 231 then AA 5506 at Charlotte
Denver → Charlotte → Memphis
Timetable, Charlotte time
15:14UA 231 from Denver at the gate
12:22AA 5506 to Memphis leaves the gate
21 h 08 apart on the timetable, overnight
AA 5506 leaves 21 h 08 after UA 231 arrives on the timetable: more than half a day, so not a connection we count.