BA 631 then BA 588 at Heathrow
Athens → London → Milan
Timetable, London time
17:00BA 631 from Athens at the gate
16:55BA 588 to Milan leaves the gate
23 h 55 apart on the timetable, overnight
BA 588 leaves 23 h 55 after BA 631 arrives on the timetable: more than half a day, so not a connection we count.