Reykjavik is 5 hours ahead of Philadelphia
Best overlap: 8:00 AM to 1:00 PM in Philadelphia is 1:00 PM to 6:00 PM in Reykjavik.
If you set up a recurring sync, 8:00 AM to 1:00 PM in Philadelphia (1:00 PM to 6:00 PM in Reykjavik) is the natural home for it. You share roughly 5 hours a day. That's enough for regular meetings, but treat the window as prime time and guard it. These times hold for most of the year, but Philadelphia's daylight saving (which Reykjavik doesn't use) shifts them by an hour twice annually.