How do I auto process customer's invoices on specific days for different customers?

Question:

We like to set our recurring invoice date to the 1st of the month and the payment terms to due upon receipt. However, some of our customers request we auto bill them on specific days of the month. For example, one customer asked that we bill for everything on the 20th of the month (even non-recurring charges). How can we do this? 

Answer:

The best way to do this is to set the due date explicitly on the invoice.  Benji Pays will wait for that due date to process the payment.