Several points to bring up since right now this system is broke....

Remove Siege scrolls completely. - This is a pvp game and castles should be open to siege 24/7.

Why do this?
This will cause the rotation of the castles more often and also give ALL players a chance to be part of a siege.

This will also limit control from dead nations and guilds that simply buy their own scrolls to avoid combat.

What else?
Each structure for the castle including walls should provide hit points or a buff for the lodestone. This will encourage players to work on the castles and help with the castle defense.

Currently in the game some guilds/nations are not building markets or farms and this has a direct impact on the economy.

Additionally removing siege timers will also encourage guilds and nations to form alliances that could help them defend and also allow world pvp to happen at any time.

Peace fund could possibly be split between the nation that claims the castle after a siege and the game could add pvp quests that can grant honor