Other people are suggesting using After to keep incrementing, but I would suggest adding a field to keep track of things (I'm assuming you're using types for your enemies.) So like in the type definition add a field called "updated" and store Millisecs() in there whenever a character updates. Then code the AI to only update if the last update was like half a second ago or something. Now you just have to make sure to stagger their initial state in order to stagger the updates.
ADDITION: oh wait from sledge's post I get what you are asking. Yeah I'm describing a different approach to the same thing he is getting at; the AI calculations for a single character still happens in a single frame, but you aren't updating all of the characters every frame.
ADDITION: oh wait from sledge's post I get what you are asking. Yeah I'm describing a different approach to the same thing he is getting at; the AI calculations for a single character still happens in a single frame, but you aren't updating all of the characters every frame.