A3 953 then BA 637 at Athens
Riyadh → Athens → London Heathrow
Timetable, Athens time
07:40A3 953 from Riyadh at the gate
20:15BA 637 to London Heathrow leaves the gate
12 h 35 apart on the timetable
BA 637 leaves 12 h 35 after A3 953 arrives on the timetable: more than half a day, so not a connection we count.