There's a separate building a little distance away from the main school building. From there we search for a route to the dorms, and position ourselves somewhere with no people. It's by the forest and is an open space that's hard to see from elsewhere.
There, we wait grandly, taking imposing poses. It's evening now. There are few passerbys. I don't have a policy of holding my duels during the evening or anything. It's because right now is when their lessons end and they're leaving the school building. By the end of the day their mana is depleted, or so my plan went.