qzjul has said the bots don't all play at the same time. http://earthempires.com/forum/post/638783/perm

edit: OH you are talking about bots logging out with random turns left over.

by the way, one thing that is bad about bots is that they buy 100 turrets at a time. It floods all my news, i could have been attacked or something and it would be hard to find because some homosexual bot has decided to buy 301 turrets thirty different times