AS 2012 then UA 3875 at Seattle
Vancouver → Seattle → Denver
Timetable, Seattle time
09:07AS 2012 from Vancouver at the gate
15:00UA 3875 to Denver leaves the gate
5 h 53 apart on the timetable
Seattle’s board gives a departure time for only about 56% of its flights, so many days show no gate time.
The last days
AS 2012 and UA 3875 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.