FB 851 then CX 252 at Heathrow
Sofia → London → Hong Kong
Timetable, London time
16:45FB 851 from Sofia at the gate
11:00CX 252 to Hong Kong leaves the gate
18 h 15 apart on the timetable, overnight
CX 252 leaves 18 h 15 after FB 851 arrives on the timetable: more than half a day, so not a connection we count.