I think the OP was questioning how the requirement to be at the airport for 8am could be right given what he considers to be the operational limitations- namely that the replacement will not be able to leave before 6, which means that it could not arrive much before 11, thereby making the 8am start improbable. I think various posters have now provided feedback and information to the effect that, for various reasons, the 8am start is very much a possibility. I advise the OP to follow the instructions on when to arrive back at SOF!