UA 3909 then UA 8253 at San Francisco
Cancún → San Francisco → Washington
Timetable, San Francisco time
15:10UA 3909 from Cancún at the gate
18:30UA 8253 to Washington leaves the gate
3 h 20 apart on the timetable
The last days
UA 3909 and UA 8253 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.