In terms of Section 13(3) of the CGST Act, 2017, the time of supply of services for remittance of tax under reverse charge mechanism shall be the earliest of the following:
(a) Date of payment recorded in the books of accounts of the recipient;
(b) Date of debit in bank account of the recipient;
(c) 60 days from the date of issue of invoice or any other document in lieu thereof by the supplier; or If it is not possible to determine the time of supply under the aforesaid clauses, the time of supply shall be the date of entry in the books of account of the recipient of supply.
In case of associated enterprises, where the supplier of service is located outside India, the time of supply shall be the date of entry in the books of account of the recipient of supply or the date of payment, whichever is earlier.
(ICAI FAQ PUBLICATIONS 06-09-2017 TIME OF SUPPLY OF SERVICES: FAQ NO. 18)