UA 3883 then B6 855 at Boston
San Francisco → Boston → Washington National
Timetable, Boston time
08:16UA 3883 from San Francisco at the gate
13:00B6 855 to Washington National leaves the gate
4 h 44 apart on the timetable
The last days
UA 3883 and B6 855 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.