DL 3990 then DL 3988 at Detroit
Louisville → Detroit → Cleveland
Timetable, Detroit time
12:04DL 3990 from Louisville at the gate
20:00DL 3988 to Cleveland leaves the gate
7 h 56 apart on the timetable
The last days
DL 3990 and DL 3988 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.