This is the default route that cycle.travel's routing engine generated for me.  It's 180 km with a computer estimated time of 11h27 minutes.

The route takes one along the Doubs, then climbs gently enough in rolling countryside, and finally into forest in the Jura mountains. It provides great views and at the time of writing (early Sept 2025) the countryside is lush and green. 

But if you are carrying luggage and are not equipped with mountain bike tyres and gearing, don't imagine there is any chance of finishing in under 12 hours, especially in the rain. In the forests the route takes off on gravel paths some of which are exceptionally steep and, if wet, very muddy: I was on a cross bike with a rack (and bags), 28 mm road tyres, and road bike gearing that can cope with most gradients on roads in the Jura: in the rain on steep muddy gravel slopes I walked, pushing the bike up hill.

Once in Switzerland, if you are worn out, there is a train service just over the border from La Cure that will do the final climb for you, and offer a choice of options: train all the way to Geneva, or exit somewhere on the descent (Saint Cergue is one possibility) to finish on two wheels. You need a ticket for both the passenger and the bike, and being Swiss, the ticket machine takes cash and credit cards.

It's a great route, but you need to be a "Mathieu van der Poel" extra-terrestrial to make it in 12 hours !