• Due Date – the date the balance is due; shown to the customer as Balance Due Date and available as the @dueDate merge tag.
• Net Days (default 15) – a grace period added to the due date. A proposal is only considered Past Due once Due Date + Net Days has passed.
• Days Before Due Date for Email Reminders (default from your kitchen setting, normally 5) – the daily reminder job emails the customer N days before the Due Date and again N days before Due Date + Net Days, as long as the proposal is Signed and Approved or Partially Paid and still has a balance.

All three are copied when you clone a proposal; recurring proposals keep the same gap between event date and due date.