AA 1997 then AA 821 at O'Hare
St Louis → Chicago → San Francisco
Timetable, Chicago time
09:00AA 1997 from St Louis at the gate
15:15AA 821 to San Francisco leaves the gate
6 h 15 apart on the timetable
The last days
AA 1997 and AA 821 weren’t both flown 15 min to 12 h apart in the last 21 days.
Statistics from past flights, not live flight information. Always check times and your connection with your airline, and don’t base travel or booking decisions on these numbers.