Washington, D.C. is 5 hours behind Reykjavik
Best overlap: 1:00 PM to 6:00 PM in Reykjavik is 8:00 AM to 1:00 PM in Washington, D.C..
Both offices are open during 1:00 PM to 6:00 PM Reykjavik time, which is 8:00 AM to 1:00 PM in Washington, D.C.. Roughly 5 hours of common time means scheduling is manageable; just avoid the very edges of the window. Heads up: because Washington, D.C. changes its clocks and Reykjavik doesn't, the difference moves by an hour twice a year. Confirm the overlap around the DST switch.