AA 250 then UA 3876 at O'Hare
Mexico City → Chicago → Miami
Timetable, Chicago time
18:59AA 250 from Mexico City at the gate
07:00UA 3876 to Miami leaves the gate
12 h 01 apart on the timetable, overnight
UA 3876 leaves 12 h 01 after AA 250 arrives on the timetable: more than half a day, so not a connection we count.