QR 3 then BA 672 at Heathrow
Doha → London → Thessaloniki
Timetable, London time
12:15QR 3 from Doha at the gate
10:25BA 672 to Thessaloniki leaves the gate
22 h 10 apart on the timetable, overnight
BA 672 leaves 22 h 10 after QR 3 arrives on the timetable: more than half a day, so not a connection we count.