Philadelphia 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 Philadelphia.
For the smoothest call, aim inside 1:00 PM to 6:00 PM in Reykjavik, i.e. 8:00 AM to 1:00 PM in Philadelphia. With 5 hours to play with, a mid-window meeting keeps things balanced for Reykjavik and Philadelphia alike. Daylight saving complicates things slightly: Philadelphia observes it, Reykjavik doesn't, so the difference flexes by an hour part of the year.