Change in tax rate fixes time of supply by the earlier of invoice issue or payment entry across the rate change. Change in the rate of tax determines the time of supply. If supply occurs before the rate change, time of supply is the earlier of invoice or payment when both follow the change, the invoice date where invoice precedes but payment follows, and the payment date where payment precedes but invoice follows. If supply occurs after the rate change, time of supply is the payment date where payment follows but invoice precedes, the earlier of invoice or payment where both precede, and the invoice date where invoice follows but payment precedes. Payment date is the earlier of book entry or bank credit; bank credit counts after four working days.