Customer Customization

Need a little direction here. I am working on a customization that
once the "customer" is changed from suspect to prospect it puts a date
in Date01. This is the easy part. The part I am having trouble with
is that they want it to set the customer back to prospect once 30 days
has elapsed from that time. I know this will not be a screen
customization, I am guessing some sort of procedure or something?