Rio de Janeiro is 8 hours behind Karachi
Best overlap: 4:00 PM to 6:00 PM in Karachi is 8:00 AM to 10:00 AM in Rio de Janeiro.
Your window to reach both cities is 4:00 PM to 6:00 PM in Karachi, which converts to 8:00 AM to 10:00 AM in Rio de Janeiro. You've got roughly 2 hours — enough for a focused daily check-in if you hold it at 4:00 PM in Karachi (8:00 AM in Rio de Janeiro).