Budapest 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 Budapest.
Your window to reach both cities is 8:00 AM to 5:00 PM in Reykjavik, which converts to 9:00 AM to 6:00 PM in Budapest. 9 hours of shared hours is more than enough — slot meetings wherever they're most convenient for the people involved. Bear in mind Budapest shifts for daylight saving while Reykjavik stays fixed — recheck these hours after each clock change.