AA 6255 then UA 3907 at O'Hare
Sioux Falls → Chicago → Washington
Timetable, Chicago time
17:29AA 6255 from Sioux Falls at the gate
12:00UA 3907 to Washington leaves the gate
18 h 31 apart on the timetable, overnight
UA 3907 leaves 18 h 31 after AA 6255 arrives on the timetable: more than half a day, so not a connection we count.