F9 3990 then DL 4173 at Detroit
Dallas-Fort Worth → Detroit → Saginaw
Timetable, Detroit time
21:43F9 3990 from Dallas-Fort Worth at the gate
21:15DL 4173 to Saginaw leaves the gate
23 h 32 apart on the timetable, overnight
DL 4173 leaves 23 h 32 after F9 3990 arrives on the timetable: more than half a day, so not a connection we count.