BA 1489 then BA 57 at Heathrow
Glasgow → London → Johannesburg
Timetable, London time
21:30BA 1489 from Glasgow at the gate
21:15BA 57 to Johannesburg leaves the gate
23 h 45 apart on the timetable, overnight
BA 57 leaves 23 h 45 after BA 1489 arrives on the timetable: more than half a day, so not a connection we count.