BA 419 then UA 959 at Heathrow
Luxembourg → London → Chicago
Timetable, London time
11:40BA 419 from Luxembourg at the gate
10:25UA 959 to Chicago leaves the gate
22 h 45 apart on the timetable, overnight
UA 959 leaves 22 h 45 after BA 419 arrives on the timetable: more than half a day, so not a connection we count.