CX 251 then FB 852 at Heathrow
Hong Kong → London → Sofia
Timetable, London time
05:25CX 251 from Hong Kong at the gate
17:45FB 852 to Sofia leaves the gate
12 h 20 apart on the timetable
FB 852 leaves 12 h 20 after CX 251 arrives on the timetable: more than half a day, so not a connection we count.