Auto-Close help please

Auto-Close help please

We are currently using version 8.0.0 Build 8016 of ServiceDesk plus and would like to setup an auto-close rule to close any requests that have been in the state of 'Waiting User' with no updates for 20 days.
 
Is this possible?
 
We can see the request closing rules but must be missing something obvious if we are able to set a counter on the waiting user time.
 
Sorry if this a silly question.
 
Any help or pointers would be great
 
Best regards
 
Paul 

      New to ADSelfService Plus?