Philadelphia is 13 hours behind Seoul

There is no standard 8-to-6 overlap. Someone joins early or late.

Seoul and Philadelphia are 13 hours apart, and that gap is wide enough that their normal 9-to-5 workdays never quite touch. If you meet regularly, fix one off-hours slot and rotate it between Seoul and Philadelphia so the burden doesn't fall on one team. These times hold for most of the year, but Philadelphia's daylight saving (which Seoul doesn't use) shifts them by an hour twice annually.