"<empire team="2" grace="99000" />"
From what I understand, grace is the time in seconds that AI teams wait until they start attacking.
E.G. if you want Team 2 to start attacking after 5 minutes, set their grace to 300 (5x60=300).
Assign different teams to different parts of your rings and give them ever increasing grace times.
In the main game options, you might have to remove the grace entry:
<dir name="AI">
<dir name="MINTICK" type="int" value="3" />
<dir name="MAXTICK" type="int" value="6" />
<!--dir name="GRACE" type="int" value="99000" /--> (Either comment this out like this, or just delete the whole line)
</dir>
Does that help? If I am wrong someone please chime in.
Thanks,
-Jamis