UA 3925 then KL 7451 at San Francisco
Denver → San Francisco → New York JFK
Timetable, San Francisco time
12:52UA 3925 from Denver at the gate
21:35KL 7451 to New York JFK leaves the gate
8 h 43 apart on the timetable
The last days
UA 3925 and KL 7451 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.