Add post dated invoice due date to Project Management add-on's invoice generation system.
Make a configuration setting in the Project Management addon so that I can set how many days after the invoice is sent that the invoice will be due on invoices created when I press "Generate Now and Send Invoice" button. When I do that now it sets the due date to today's date, meaning that the next day the client receives a past due warning email.
Allow me to set a 7, 14, etc. day later due date on invoices generated through this add-on.