How to invoice after X days?

We have a "if you don't like it, send it back" policy. So we ship the products, then when the customer receives the goods, he checks them out and if he likes them, he then pays the full invoice. If the customer is not satisfied with any of the products, he can make a partial or full return of the shipment and he gets a payable invoice on the items he didn't return. How can we achieve this workflow in Zoho CRM?