OS 553 then FR 8837 at Fiumicino
Vienna → Rome → Zagreb
Timetable, Rome time
14:15OS 553 from Vienna at the gate
12:00FR 8837 to Zagreb leaves the gate
21 h 45 apart on the timetable, overnight
FR 8837 leaves 21 h 45 after OS 553 arrives on the timetable: more than half a day, so not a connection we count.