I accept your feedback about the times, So what do you propose instead?
I like the post someone said about having a 1% exp/drop buff for every 24 hours you hold it. Capped at 10%.
I would say have it so you can war once every 12 hours ish, but the attacking guild can decide the start time. If you submit for war, but are unsuccessful then you have a 36hour cooldown from when the war ended until your guild can resubmit.
Once a war has ended, any guild can submit for the next war, but the start time cannot be until 12-24hours hours later, giving the holding guild time to prepare.
For example, Guild A goes to SW at 8pm today to declare war, you can then choose a start time between 8am and 8pm the following day.
If guild A schedules for 10am the following day, then guild B turns up at 9pm today to declare, they see a war is scheduled, then they will be able to schedule one from 11pm-11am the next day.(12 hours after the scheduled war is due to end). If guild A schedules for 6pm, then guild B will not be able to schedule a war prior to that, even though it is within 12hours. (First come first served).
If you are the defending guild and lose you dont have a 36hour cooldown, you can declare for the next available slot as above
Keeping the requirement of 20+ guild members, and unable to recruit for declaring guild is a good idea. I would also add in if the holding guild has made an alt guild and keeps submitting to block up the schedule then there will be repercussions (lose the war/unable to submit for a week)
How will the first war be determined? A rush to SW to submit first? Given a relic is no longer required, whoever logs in first looks guaranteed to take the castle.
Also as a difference to the enter the castle, I think it would be good to have a monument to defend.
This would be similar to EC, in that if no attackers/neutral are near it then it is hidden, once attackers/neutral are within range it will appear and can be attacked by both melee and range attacks. If only defenders/allies are near then it will be hidden. (May be worth introducing an ally system) The monument does not attack, while it is hidden it slowly regens, while it is up it does not regen and cannot be healed.
Defending guilds can upgrade the monument, materials can be gathered from SW cave only, the exp will be similar to PB, but low gold drops and only SW materials drop. (things like wood/ores used to upgrade) Upgrading it will just make a level'd version of the monument
When a guild takes over, the monument is reset to the basic version. Gates and archers can still be purchased by the defending guild.
Further idea on how to take castle.
1 main totem/monument in the middle that needs to be destroyed in order to take the castle.
There are 4 sub totems around it giving a 25% defence boost to the main monument.
These monuments do not regenerate any health. All totems are visible throughout the siege
These can be upgraded by the defending guild to boost defence.
There all also 10 nodes within the castle, 5 defensive and 5 damage based. These give a 10% increase per node to attack/defense stats for players. These cannot be upgraded
At the start of the siege the nodes belong to the defending guild. Once the siege starts the attacking guild can take control of these nodes (hitting them like trees to dmg them), killing the node transfers the buff from the defending guild to the attacking guild. The node can be retaken every 5minutes, during this cooldown time it is immune to damage, but the buff applies during the cooldown. The buffs apply during the war and you dont need to be in a certain range to benefit
The sub totems give 25% defence to the main totem, attacking guilds can then look to either take these down to make taking the main totem easier, or go straight for the main totem. Sub totems do not respawn during the war. they require repairing outside of war in order to work on the next war.
the main totem does not require repairing between wars
Totems are damaged like normal mobs (not individual hits like the nodes)