The rice that's prepared at dawn by the village are provisions for the army. The army is scheduled to arrive right after dawn, so all of the village's provisions for them have to be ready by then.
Once all of the provisions are ready, the soldiers show up in their row (りょう) boats and load it all up. But they aren't done there. "Rice isn't enough, we need roe (ろう) so we will have the strength to row our row boats back." And so the village brings them all of their roe too.