I think it would be good to have a few breaks on the way down to allow your group get back together. My first suggestion is just after point H on the map, there is a cafe after the tennis court near the marina;
HERE
The second for lunch is Sille-le-Guillaume, just after point P on the original Map. We'll just find some parking somewhere and try to find somewhere to eat, how hard will it be to spot some early '11's!
We would then have about an hour to the campsite.