Vienna is 6 hours ahead of Ottawa
Best overlap: 8:00 AM to 12:00 PM in Ottawa is 2:00 PM to 6:00 PM in Vienna.
Plan around 8:00 AM to 12:00 PM in Ottawa, which is 2:00 PM to 6:00 PM in Vienna, to catch everyone during office hours. Since Vienna is 6 hours ahead of Ottawa, the workdays overlap by around 4 hours; 8:00 AM in Ottawa (2:00 PM in Vienna) makes a reliable recurring slot.