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.
"Invoice": This indicates the purpose of the commercial document and should be placed near the top of the page. Name of your business: Format in bold and place at the top of the page. Include your company logo for a branded look.