Karachi is 2 hours behind Hanoi
Best overlap: 10:00 AM to 6:00 PM in Hanoi is 8:00 AM to 4:00 PM in Karachi.
Your shared working hours run 10:00 AM to 6:00 PM in Hanoi (8:00 AM to 4:00 PM in Karachi). Scheduling is forgiving here: with 8 hours of overlap, a missed slot just means picking another one the same day.