UA 3917 then VS 1906 at San Francisco
Houston → San Francisco → Seattle
Timetable, San Francisco time
17:45UA 3917 from Houston at the gate
20:59VS 1906 to Seattle leaves the gatealso SK 3106, SK 3470, DL 3991
3 h 14 apart on the timetable
The last days
UA 3917 and VS 1906 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.