Net Days (found next to Due Date on the proposal, default 15) is the number of extra days of grace given after the Due Date before the balance is treated as overdue. Sprwt's daily job compares Due Date + Net Days to today: once that date has passed for a Signed and Approved or Partially Paid proposal, the status automatically changes to Past Due. The same Due Date + Net Days value is also used to time the second automatic payment reminder (the first goes out Email Reminder Days before the Due Date, the second that many days before Due Date + Net Days). The Account Receivable Report shows Net Days as its own column so you can see each event's grace period at a glance.