UA 6138 then AA 5599 at Charlotte
Houston → Charlotte → Springfield
Timetable, Charlotte time
15:54UA 6138 from Houston at the gate
15:42AA 5599 to Springfield leaves the gate
23 h 48 apart on the timetable, overnight
AA 5599 leaves 23 h 48 after UA 6138 arrives on the timetable: more than half a day, so not a connection we count.