You can complete this quest once per day. Timer is reset on 6.30 a.m. If the period of Seed siege is different, Defend the Hall of Suffering quest will be taken instead.
When the twins are defeated, the party leader need to talk to Officer Tepios so all the participants could get their reward. You can open your chest by double-clicking it in your inventory.
Reward
You reward depends on how much time you’ve spent to complete the task in the Hall of Suffering.