UA 901 then BA 418 at Heathrow
San Francisco → London → Luxembourg
Timetable, London time
07:25UA 901 from San Francisco at the gate
07:10BA 418 to Luxembourg leaves the gate
23 h 45 apart on the timetable, overnight
BA 418 leaves 23 h 45 after UA 901 arrives on the timetable: more than half a day, so not a connection we count.