Hanoi is 2.5 hours behind Adelaide
Best overlap: 10:30 AM to 6:30 PM in Adelaide is 8:00 AM to 4:00 PM in Hanoi.
The best time to meet is 10:30 AM to 6:30 PM in Adelaide, which is 8:00 AM to 4:00 PM in Hanoi. 8 hours of shared hours is more than enough — slot meetings wherever they're most convenient for the people involved. One seasonal catch: Adelaide springs forward and falls back, but Hanoi doesn't, so the gap changes by an hour for several months of the year.