When we did this 3 years ago, we went to breakfast as usual, then waited for our luggage group (character) to be called. Once we got our luggage, we went right out to the bus, and once the bus was full, it was on its way to London. As for timing, it all depends on early vs late dining, which dictates your breakfast time, then which luggage group you are assigned to. If I remember correctly, we were off the boat around 8:30 am to 9:00 am, we had main/early dining, and hit the airport somewhere around noon. Because Dover is a small terminal, they can't stage all the luggage at once.