Time of supply under forward charge: earliest of invoice issuance, payment receipt, or accounting entry determines tax point. Time of supply under Section 12(2) is the earliest of invoice issuance (or last date for issuance under section 31), receipt of payment to the extent it covers the supply, entry in books of account, or bank credit date. For regular taxpayers the relevant dates narrow to invoice issuance or the last date for issuance; composition taxpayers and suppliers of specified actionable claims follow general provisions except as modified by notifications. Partial advances or partial invoicing fix the tax point only to the covered portion of supply.