Well, there's this thread you might want to read:
https://www.vbulletin.com/forum/show...ron-VBIV-13733 . In post 6 Wayne posts a command line you can use in a cron job, and he mentioned that if you just set it to run every 30 seconds then it should take care of the problem of running it multiple times (because it doesn't do anything if there's nothing to do, so apparently it doesn't matter much if it's run too often). Also if you do that you could remove the cron image from your footer.
Anyway, later in that thread Wayne talks about a way to specify the specific task you want to run, if you want to go that route.