BA 56 then BA 1456 at Heathrow
Johannesburg → London → Edinburgh
Timetable, London time
04:55BA 56 from Johannesburg at the gate
17:05BA 1456 to Edinburgh leaves the gate
12 h 10 apart on the timetable
BA 1456 leaves 12 h 10 after BA 56 arrives on the timetable: more than half a day, so not a connection we count.