PTO Accrual Formulas

We have a requirement to allow certain emplpyees to use up the carryover residual by the end of the 6 th month following carry over or they are to stop accruing in the 7 th month. 

We have that formula written using this formula;

If (Period_ED > l_stop_accrual_date )

   THEN   

   (

       IF( (Other - Absence) > 0)

        THEN

 period_accrued_pto = 0

    ELSE

 period_accrued_pto = period_accrued_pto

)

Now once the employee (other - absense) <=0 they can not start accruing again but not until the 1st of month following.

Any suggestions on how to do this?

thanks,

Linda