Paul,
We are booked on the 10:40 outward sailing on Friday and 16:00 return on Sunday. Having taken the best part of half an hour to convince the Stena Line system to take my booking, I don't want to mess with it too much!
We are leaving Bedford at 6.45 which should get us to Harwich an hour before the sailing. You could head over to Bedford Thursday evening if you wanted to - beer, movies and crashing space are available.