AA 517 then DL 1655 at San Francisco
Chicago O'Hare → San Francisco → Boston
Timetable, San Francisco time
11:31AA 517 from Chicago O'Hare at the gatealso QF 4687
21:54DL 1655 to Boston leaves the gatealso VS 2642, LA 6808
10 h 23 apart on the timetable
The last days
AA 517 and DL 1655 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.