Work Flow Alert Email Functionality for Billing Block Removal in Order

Dear Experts ,

My requirement is that , the billing block need to be removed in the contract sales document on the due date .

Business needs an automatic workflow based E-mail alert on the due date. , so as to remove the block.

The table FPLA/FPLT has the billing plan numbers and the due dates contained.

Any date alert email ideas , can anybody advise ?

Thanks in Advance

Karthik