Reporting a number of days the status of a job was running between 2 custom dates.

I like that possibility. 
  
During the wait for assistance, I created 2 new Formula Date fields.   Reporting Start Date and Reporting Stop Date.   

The Reporting Start Date field looks at if the actual Start Date field is >30 days ago, it will use 30 days ago as the Reporting Start Date. 
         My formula   
  Max([Start],(Today()-Days(30)))

The Reporting Stop Date will look at the Actual End date, and if it is populated it will use it, otherwise it will use Today. 
         My formula
Min([End],Today()) 

Then, I set up to filter the jobs to those that had a Start or End date that is within the last 30 days.    

So far, I think it is working correctly.