When invoices are created you can choose to send them right away, or select a date for them to be sent. Follow the instructions in this article on how to create an invoice.
Under Set Up Custom Billing Schedule choose the Start Date and Due Date. The Start Date will be the day the invoice is sent to the member.
Once the invoice is sent on the Start Date, members will be sent a statement of account on the 3rd and 15th of every month until their balance is paid.