UA 1591 then B6 1234 at San Francisco
San Antonio → San Francisco → Boston
Timetable, San Francisco time
11:02UA 1591 from San Antonio at the gate
14:50B6 1234 to Boston leaves the gate
3 h 48 apart on the timetable
The last days
UA 1591 and B6 1234 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.