Radial Delay is an After Effects script that takes selected layers and delays them in time based on their distance to the center of a composition. If you haven't yet, check out the video above for more information on how it works. You can also check out the tutorial for the Radial Delay expression. The script renders much faster, and it'll save you a lot of time if you need to do a similar effect.
This download comes with the script and a user guide