Hamburg is 6 hours ahead of Philadelphia
Best overlap: 8:00 AM to 12:00 PM in Philadelphia is 2:00 PM to 6:00 PM in Hamburg.
Shoot for 8:00 AM to 12:00 PM in Philadelphia; your Hamburg colleagues will see that as 2:00 PM to 6:00 PM. Since Hamburg is 6 hours ahead of Philadelphia, the workdays overlap by around 4 hours; 8:00 AM in Philadelphia (2:00 PM in Hamburg) makes a reliable recurring slot.