Warsaw 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 Warsaw.
Shoot for 8:00 AM to 12:00 PM in Ottawa; your Warsaw colleagues will see that as 2:00 PM to 6:00 PM. Since Warsaw is 6 hours ahead of Ottawa, the workdays overlap by around 4 hours; 8:00 AM in Ottawa (2:00 PM in Warsaw) makes a reliable recurring slot.