Flying YYZ-ATL-HNL. Flight from YYZ leaves @ 6:15 AM and flight from ATL leaves at 9:50 AM. When I check in tomorrow morning, I know I can change seats for YYZ-ATL. Will I be able to do the same for ATL-HNL at 6:15, or do I need to wait until 9:50 ? Just trying to get a preferred aisle seat for the 9+ hr flight.