How can Billing and Due Calendar setup testing be done with past and future dates?

How do you test the Billing and Due Calendar setup with past and future date information?  For each term, we have 3 different registration periods, each with a different due date.  I'm trying to test to see if my setup is correct.  I have changed the enrollment dates to both past and future dates, but once I process the tuition calc, it only recognizes today's date.  We are on PS 9.0.  Any insight would be greatly appreciated.