I usually send about 10 days before payment due (2 weekends to sort it) . I have occasionally had emails in advance of this asking whne we are going to send the final invoice.
1 week before due for guests paying by cheque and 3-4 days for those sending a bank transfer. Sometimes they beat me to it and very occasionally I have to chase them after the due date.o
Jo
Joint owner of Baker's Cottage in Chester & Chandler's Cottage in Sidmouth