On either airline you should be able to eat whenever you want. That said, whenever I've taken this flight, I've eaten dinner at a normal hour, either at home, in a restaurant, or in the lounge, and have put myself to sleep the moment the wheels lifted off the ground and have done my best to remain asleep until the announcement that we need to prepare for landing. In dozens of these overnight flights to London, I don't think I've once consumed any food on board.