I used to participate in Lineage 2 sieges, and now I understand why they were time limited in the weekend, after which the winner takes control of the region castle and it's benefits.
There was an NPC in front of each castle where alliances would public subscribe to attack or defend. There was also NPCs defending during early battle, but once the gate was down it was pure pvp until the throne room.
Everyone could organize their lives to those couple hours without loosing sleep or work, and makes sense IRL.