FB 851 then LX 355 at Heathrow
Sofia → London → Geneva
Timetable, London time
16:55FB 851 from Sofia at the gate
14:25LX 355 to Geneva leaves the gate
21 h 30 apart on the timetable, overnight
LX 355 leaves 21 h 30 after FB 851 arrives on the timetable: more than half a day, so not a connection we count.