AA 9928 then UA 3909 at O'Hare
New York LaGuardia → Chicago → San Francisco
Timetable, Chicago time
06:45AA 9928 from New York LaGuardia at the gate
19:30UA 3909 to San Francisco leaves the gate
12 h 45 apart on the timetable
UA 3909 leaves 12 h 45 after AA 9928 arrives on the timetable: more than half a day, so not a connection we count.