DL 977 then UA 3906 at San Francisco
Boston → San Francisco → Chicago O'Hare
Timetable, San Francisco time
11:41DL 977 from Boston at the gate
19:30UA 3906 to Chicago O'Hare leaves the gate
7 h 49 apart on the timetable
The last days
DL 977 and UA 3906 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.