It’s important to note that you can do a hit on each castle and call it a day, but that’s bricking your runs and your guild score.
Each castle is divided into outer gate, inner gate and a boss, each stage granting higher rewards for you and the guild.
So if you hit each castle one time, you are getting way less rewards than if you do three hits per castle.
This system rewards organization inside the guilds so everyone is attacking the same 2 castles.
You can check the guild to see what castles people are hitting which helps organizing and managing guilds pretty easy.
To switch to this view, use the button top right, besides the edit icon.