BA 54 then BA 870 at Heathrow
Johannesburg → London → Budapest
Timetable, London time
06:45BA 54 from Johannesburg at the gate
19:25BA 870 to Budapest leaves the gate
12 h 40 apart on the timetable
BA 870 leaves 12 h 40 after BA 54 arrives on the timetable: more than half a day, so not a connection we count.