I'm not exactly sure quite how to ask this question, but I'll describe some experiences recently while playing single-player games against the AI (usually on Medium, sometimes on Hard).
I've noticed that the AI seems to roughly match my pace of development. When I've developed more slowly, the AI has taken longer to go to Phase III and attack me. Whereas, when I develop quickly and expand my territory more quickly, the AI attacks earlier and develops more quickly. Meanwhile, when I set up games and watch the AI play another AI on Hard or Very Hard, the games seem to drag on forever and the AI develops pretty slowly.
Are these just coincidences? Or does the AI develop more quickly when its opponent does?