Nick, We have used this route for the past few years, it is exellent!, I cant remember what time we were called but Im sure it wasnt that early, you disembark aat about 8.15 french time and it is straight onto dual carrigeway, urban at first, if you are heading south, there is a right turn onto another dual carrigeway signed "Rennes", there is a filling station for cheap french diesal about 4-5 miles
outside St Malo, on the right, you cant miss it, with the early start. For us it is by far and away the best route, and no tolls until Nantes. We find it completely hassle free!!
We'll be using it again next year
JimF