Assistance with Comp Time accrual setup

We have implemented a comp time policy and I was wondering if anyone else has one similar that could assist in setting up the accrual portion. The policy states that an employee can be awarded up to 40 hours max and that it has to be used within 6 months and if not used, it's lost.

I have the 40 hours annual limits set up the accrual and the pay type. Is there a way to set up an expiration date on the accrual knowing that hours could be awarded multiple times within the year?

Thanks for any assistance!

Scott Whitlock