While the trebuchets took a long time to be moved, that time wasn't infinite. The first projectiles were sent soaring through the air mere moments after the guild had decided on a plan of action.
"Take aim!" Zyviss commanded, pulling back his bow—a fire arrow from the Elemental Quiver loaded on string. Unsure how much power would be required to destroy the projectiles, they were erring on the side of caution.
Sadly, they didn't even know what was flying towards their castle. It looked like a round boulder, but due to the distance, they couldn't really see more than that. Eldrian had, however, informed them that the builders were magically empowered. Similar to the ballistae bolts they used. Explosions were, thus, expected.