DL 541 then UA 4541 at Dulles
Seattle → Washington → Buffalo
Timetable, Washington time
00:20DL 541 from Seattle at the gate
22:19UA 4541 to Buffalo leaves the gate
21 h 59 apart on the timetable
UA 4541 leaves 21 h 59 after DL 541 arrives on the timetable: more than half a day, so not a connection we count.