Portland is 9 hours behind Warsaw
Best overlap: 5:00 PM to 6:00 PM in Warsaw is 8:00 AM to 9:00 AM in Portland.
Target 5:00 PM to 6:00 PM in Warsaw, which lands at 8:00 AM to 9:00 AM for the Portland side. Portland is 9 hours behind Warsaw, so common hours are scarce (about 1 hour). Lock the slot, keep it short, and follow up in writing.