Warsaw is 1 hour ahead of Reykjavik
Best overlap: 8:00 AM to 5:00 PM in Reykjavik is 9:00 AM to 6:00 PM in Warsaw.
Target 8:00 AM to 5:00 PM in Reykjavik, which lands at 9:00 AM to 6:00 PM for the Warsaw side. Warsaw is 1 hour ahead of Reykjavik, but with 9 hours of common ground you can hold morning or afternoon meetings without anyone working odd hours. Daylight saving complicates things slightly: Warsaw observes it, Reykjavik doesn't, so the difference flexes by an hour part of the year.