I am transferring some information about the most logical flight from HoChiMinh City to Phnom Penh: VN670 0730 0820 SGN PNH.
Teams began leg 3 between 545am and 629am on the boat, then had a 2 hour taxi ride to HCMC, then the water puppets, then transportation to the post office, then transportation to their DETOUR of choice, the DETOUR itself, then transportation to ROADBLOCK, the ROADBLOCK itself and transportation to the pit stop. They should reach the pit stop between 10am and noon. Add 12 hours for a standard pit stop and you have teams getting to the HoChiMinh City airport around midnight. They will have a long wait until the first flight at 0730, typical of Amazing Race legs when bunching is paramount.