A3 977 then A3 982 at Athens
Belgrade → Athens → Sofia
Timetable, Athens time
19:00A3 977 from Belgrade at the gate
18:50A3 982 to Sofia leaves the gate
23 h 50 apart on the timetable, overnight
A3 982 leaves 23 h 50 after A3 977 arrives on the timetable: more than half a day, so not a connection we count.