The invoice due date is used to determine which pay period submitted invoices will be processed within. In order to receive payment in a timely fashion, make sure you submit your invoice before the displayed due date and time. Your submitted invoices will most likely not be reviewed until the invoice due date.
If you attempt to submit an invoice on the due date, but passed the due time, the application will still let you submit the invoice, but will also display a warning. The warning will inform you that your submitted invoice will not be processed within the current pay period, and will have to wait to be processed until the next pay period: