The Carthaginians should be planning out their manoevers for the night. But the idea was for the Romans to deploy their camp before any scouting operations are carried out by either side.
The flow goes something like this. The Romans will set up their camp and try to cross the river in a way to best protect themselves during the night. The scouting scenario will then play out where the Carthaginians and Romans do their best to discern what the battlefield will be, what the enemy have got with them, positions, etc. After that, both sides should submit their plans for deployment and a rough battle plan for the next day, based on what their commanders would be able to predict. The Carthaginian plan should be as close to what Hannibal actually did as possible, modified only to adjust if the Romans have done something unexpected. So even if the Carthaginians botch the scouting, Hannibal would probably still plan something like Cannae, as he would have knowledge of his opponent from the previous skirmish. The Romans are only restricted by their commander's knowledge, and by the capabilities of their soldiers.
So once the Romans are ready, both sides can make their opening moves. Onus is on the Romans to set up camp at the moment. Of course, both sides should consider the necessity of scouting. The Carthaginians historically harassed the Roman water carriers as well prior to the battle, so this is something the Carthaginians should plan to do even if they have all the information they need.
Sorry, we could have explained things better. Romans, you also need to consider water. Carthaginians, you have to work out the best way to disrupt that water supply.