CA 985 then UA 8222 at San Francisco
Beijing → San Francisco → Boston
Timetable, San Francisco time
09:30CA 985 from Beijing at the gate
13:15UA 8222 to Boston leaves the gate
3 h 45 apart on the timetable
The last days
CA 985 and UA 8222 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.