Time of supply rules determine whether invoice or payment fixes tax liability after a change in tax rate. Change in tax rate determines the time of supply by reference to invoice issuance and receipt of payment. If supply precedes the rate change, the time of supply is the earlier of invoice date or payment date where both occur after the change; otherwise the invoice date or payment date applies depending on which occurred first. If supply follows the rate change, parallel rules assign time of supply to payment date or invoice date according to their sequence. Receipt is treated as the date of bank credit when credit arises after a brief banking interval, and 'date of receipt of payment' means the earlier of books entry or bank credit.