I did it two years ago with someone who had just taken up cycling, and hadn't done enough prep! It was slow going as I was waiting up each hill for her, and we ended up only doing the short route. Must admit would have hated it if I was just starting cycling, but with any miles behind you its a blistering lovely ride through some quiet rural french country roads, no bothers from cars (they will hang back an unnerving amount of time actually) and some nice hills.
My friend ended up calling the broom wagon up, while I set off to the last 15 miles as fast i could so I didn't miss the last ferry, they were packing up all the
Wiggle paraphernalia when I arrived!
To note a few things:
*As others said, VERY early start. You need to be at the car park, unpacking your bike from 5am.
*The last 6 miles is flat, before that is the biggest hill of the ride, the Escalles Hill. You will go down it on the way out, take note and save some!
* The ferries leave at their respective times, regardless of any delays you had going outbound. You may not have the full 7 hours to complete the route. Shouldn't be an issue depending on your ability.
*The police escort from the ferry to the car park is very cool!
Couldn't get my cycling mate interested in doing it so swerving it, but is on my list of things to do again, so I can have a proper go at it.