filling time before night crossing from caen

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We're spending the 2nd of our 2 weeks in France this August in the Vendee area and have booked an ovenight crossing back from Caen at 23.30. So we have  about a 4 hour journey, and will have to leave the site by midday-ish I guess. We're new to caravanning
and this is our 1st venture abroad - so not sure how we're going to fill the extra time, like how hard is it going to be to park up somewhere and visit attaractions en route?  Has anyone else done this particular route and how did you handle it? Should we
pay for an extra night and just leave the site later?  Appreciate any tips

thanks