[kh99]

You'd have to do some coding, I think. If you look at admincp/misc.php and find the section labeled "Start update user" you can see how it's done when you do it from the Maintenance menu, so you could use that code. It is written to do only a certain number of users per page so you'd have to figure out how to deal with that.

And you could either create your own php file in includes/cron and create a scheduled task for it, or you could create a plugin using hook cron_script_cleanup_daily or _hourly if you don't want to go through the trouble of making your own script.