I have a small pay for use web app.

I would like to allow people to trial the app before they pay.

To do this, I would like to have a system where temporary user accounts are created, then deleted again after 30 minutes or so.

The first thing that comes to mind is adding a column "isTemp" of type TINYINT to the accounts table, then setting a cronjob to execute the query "DELETE FROM accounts WHERE isTemp = 1" every 30 minutes.

However... I am a bit nervous about this. I have fears of waking up in the morning to find the entire accounts table empty. I realize this may be an irrational fear, but I don't like scheduled DELETE statements coming near the accounts table. :) 

What are thoughts on this? Is this the way it should be done? Or should I rethink this?

Thanks (in advance) for your help.