Not looking to eat on the boat, just a cruise at dusk to see Paris from a different angle.
What's dusk? Sunset at the solstice is about ten at that latitude. Nautical twilight will end about an hour and a half later. If you've bought a batobus ticket for about fifteen euro, it's good all day/night, but they shut down at nine-thirty in the summer. Other than that, pick the cheapest one. They all follow exactly the same route.