UA 4500 then BA 216 at Dulles
Detroit → Washington → London
Timetable, Washington time
21:17UA 4500 from Detroit at the gate
18:05BA 216 to London leaves the gate
20 h 48 apart on the timetable, overnight
BA 216 leaves 20 h 48 after UA 4500 arrives on the timetable: more than half a day, so not a connection we count.