UA 421 then DL 8841 at Dulles
Denver → Washington → Toronto Pearson
Timetable, Washington time
21:30UA 421 from Denver at the gate
16:00DL 8841 to Toronto Pearson leaves the gate
18 h 30 apart on the timetable, overnight
DL 8841 leaves 18 h 30 after UA 421 arrives on the timetable: more than half a day, so not a connection we count.