WMD was in the desert on Entropy. I remember fighting against them as they were clearing it out. I showed up to help 13th Legion with a defensive bane against WMD in the desert and was warned there would be repercussions. WMD kept that promise!
EDIT: Searched around and found a screenshot of the Entropy map.
The point of the siege window is to give people a chance to fight to defend their assets. Without a siege window people tend to destroy assets while the owners are asleep. or otherwise unable to play. It is enough for the structures to be protected, it is not necessary to also make bases into safezones where people don't have to worry about PvP.
This mechanic is familiar to anyone who played Shadowbane and it works.