BA 673 then BA 1494 at Heathrow
Thessaloniki → London → Glasgow
Timetable, London time
21:45BA 673 from Thessaloniki at the gate
18:55BA 1494 to Glasgow leaves the gate
21 h 10 apart on the timetable, overnight
BA 1494 leaves 21 h 10 after BA 673 arrives on the timetable: more than half a day, so not a connection we count.