UA 6138 then AA 3939 at Charlotte
Houston → Charlotte → Key West
Timetable, Charlotte time
15:54UA 6138 from Houston at the gate
15:40AA 3939 to Key West leaves the gate
23 h 46 apart on the timetable, overnight
AA 3939 leaves 23 h 46 after UA 6138 arrives on the timetable: more than half a day, so not a connection we count.