Randomly generate shapes

Hey all, I have been trying to accomplish randomly generating a shape such as a circle for a defined amount of time at a random x and y coordinate. I want to be able to add more random circles based on how a number I set. I have been struggling to think out of the box on this one and not getting anywhere. I thought of using a noise chop for the random x and y coordinates, but how to get them to appear and fade is beyond me. Any nudge in the correct direction?

check out the eventCHOP and, thats the most important: instancing!

So I have my grid made up. So say I only wanted a few on the circles drawn at any given time, how best to accomplish that? I try searching for tutorials but not finding anything as it directly relates to what I want.

Thanks for the reply also!