Can I force imagecache to update at certain intervals?

On the webcomic site I'm developing (which hosts three webcomics) I use imagecache to display thumbnails of the three most recently published webcomics. The setup works great when I want to publish a webcomic immediately, but if I "queue" the webcomic (if I set it up so that it is published at a future date -- i.e., if on 7/2/2007 I create a webcomic node set to appear on 7/3/2007), imagecache doesn't update the thumbnail with the latest comic when the queued node appears.

In order to get imagecache to update, I need to go to the settings page and click the "update preset" button for the preset in question -- or, I've also learned, I can go into the view I created for the thumbnail and save the view without altering it in any way. In either case, THEN the thumbnail updates properly.

I'm not sure what to do about this. Is there a way to specify that imagecache forces itself to update at specific intervals, or whenever a cron job is run, or anything like that?

(I have the same problem with 5.x-1.3 and the latest dev version).