How do we compute GST liability on supplies which are liable to tax under reverse charge?

1. Separate provisions had been provided under the erstwhile service tax laws to
   determine the service tax payable on reverse charge mechanism which is linked to date of payment to the service provider unless the payment is made within 3 months of the date of invoice.
2. However, such provisions are not there in the CGST Act, 2017. Accordingly, general provisions relating to change in rate of tax shall be applicable in
   determining the appropriate rate of tax

(ICAI FAQ PUBLICATION 06-09-2017 : Time and Value of Supply -FAQ NO. 35)