They spent the night in camp and only acted the following day, in the evening.
The first part of the plan was William's. Deep down, he didn't want to do it. It was risky, and there were no direct benefits for him. What would it even change if they succeeded in taking over the fortress? Why was he working for these people at all?
The only reason was the roleplay aspect of that dungeon floor—but even then, he wasn't sure if he should just follow the script or try to act differently. Could he achieve different results by doing so?
Anyway, when night fell, William grabbed a sack filled with bombs—basically flasks packed with explosive material. The alchemists had crafted them.
Then, he made his way to the fortress's underground tunnels. The entrance was well-hidden by thick vegetation, so unless someone actively chopped through the greenery, it would be nearly impossible to find.