Philadelphia is 11 hours behind Jakarta
There is no standard 8-to-6 overlap. Someone joins early or late.
Because Philadelphia is 11 hours behind Jakarta, the two offices are essentially never open at the same time. If a live call is essential, aim for the very start or very end of a workday in one city and accept it'll be off-hours for the other. Daylight saving complicates things slightly: Philadelphia observes it, Jakarta doesn't, so the difference flexes by an hour part of the year.