If you choose the 8km tour, start whenever you want from Collias in between 9 am to 4pm (5pm in july and august). Then paddle down to Pont du Gard and get your shuttle back to your car.
Shuttle back start at 12am until 7pm with an every hour rotation.
Duration of the tour is about 2 hours on the water + the time for yourself (picnic, siesta, selfies etc…)
Advices : during summer plan half a day and if like calm atmosphere plan to come in the early morning (9am not 6!!).