AA 2253 then UA 3876 at O'Hare
San Francisco → Chicago → Miami
Timetable, Chicago time
23:55AA 2253 from San Francisco at the gate
21:00UA 3876 to Miami leaves the gate
21 h 05 apart on the timetable, overnight
UA 3876 leaves 21 h 05 after AA 2253 arrives on the timetable: more than half a day, so not a connection we count.