Adelaide is 18.5 hours ahead of Portland
Best overlap: 1:30 PM to 6:30 PM in Portland is 8:00 AM to 1:00 PM in Adelaide.
For the smoothest call, aim inside 1:30 PM to 6:30 PM in Portland, i.e. 8:00 AM to 1:00 PM in Adelaide. Since Adelaide is 18.5 hours ahead of Portland, the workdays overlap by around 5 hours; 1:30 PM in Portland (8:00 AM in Adelaide) makes a reliable recurring slot. Because Adelaide is on the next day, weekend boundaries can shift; check that neither side is meeting on their day off.