The due date for the invoice is totally up to you, however, most invoicing systems are set up on a 30 day, 45 day or 60 day timeframe. You can also make the invoice "Due upon receipt," where the recipient is required to pay the invoice promptly.
Along with the payment terms, you can specify whether you charge a late fee for invoices paid past their due dates. Some freelancers like this option, to enforce getting paid on time. You may also want to include your tax ID number in this area for tax purposes.