As a window cleaning business, we have LOTS of recurring invoices. The only problem being that the jobs cannot always be done exactly X weeks after the previous invoice date. It could be a few days after. An option to have a 'floating' period that adjust to the last invoice date would be a fantastic feature. The 'Copy' feature is too laborious for so many invoices. So a user could set up a recurring invoice at 4 weekly intervals, but each subsequent recurring invoice would be created 4 weeks after the last invoice date, rather than fixed.