With my above setup 5% would through the balance out of whack. Remember I mentioned the idea of having alliances. So that guilds can help each other maintain overall land control. This way it's not necessary to have all of your guild on 24/7, and other guilds will be willing to help out even though they don't have direct benefit from your base and towers, it will keep the overall land control to the side of whatever faction you belong to.
But, it does get a bit unfair for small orgs, seeing as there is not enough land to really go around. Interesting dilemna.
Maybe have it 25% all of the time.. with 5% on the weekends