Is there any form and time limit prescribed for furnishing the explanation for discrepancies noticed during scrutiny

The registered person shall furnish an explanation for the discrepancy in
FORM GST ASMT-11 to the proper officer within such time, not exceeding thirty days from the date of service of the notice or such further period as may be permitted by the proper officer. Where the explanation furnished by the registered person or the information submitted thereby is found to be acceptable, the proper officer shall inform him accordingly in FORM GST ASMT-12.

(ICAI FAQ PUBLICATIONS 06-09-2017 SCRUTINY OF RETURNS: FAQ NO. 16)

How will a return under scrutiny be processed and what will be the mode of intimation of discrepancies

Where any return furnished by a registered person is selected for scrutiny, the proper officer shall scrutinize the same in accordance with the provisions of section 61 with reference to the information available with him, and in case of any discrepancy, he shall issue a notice to the said person in FORM GST ASMT-10, informing him of such discrepancy and seeking his explanation and where possible quantifying the amount of tax, interest and any other amount payable in relation to such discrepancy.

(ICAI FAQ PUBLICATIONS 06-09-2017 SCRUTINY OF RETURNS: FAQ NO. 15)

What action may be taken by the proper officer in case no satisfactory explanation is sought after the discrepancies are bought to the notice of the registered person

In case, after accepting the discrepancies, no satisfactory explanation is furnished within a period of thirty days or such further period as may be permitted, proper officer may:
(a) Initiate Audit of accounts by the tax authorities under Section 65; or
(b) Initiate special audit under Section 66; or
(c) Initiate inspection, search and seizure under Section 67; or
(d) proceed to determine the tax and other dues under Section 73 or Section 74.

(ICAI FAQ PUBLICATIONS 06-09-2017 SCRUTINY OF RETURNS: FAQ NO. 14)

What does scrutiny of returns mean under CGST Act, 2017

The CGST Act, 2017 empowers proper officer to scrutinise the return and related particulars furnished by the taxable person to verify the correctness of the return and inform him of the discrepancies noticed, if any, in a manner as may be prescribed. In case of any discrepancies, the proper officer should seek explanation from registered person. On receipt of satisfactory explanation, the proper officer is not required to take any further action. In the event, after accepting the discrepancies, no satisfactory explanation is furnished within a period of thirty days or such further extended time. If the taxable person fails to take the corrective measures in the return for the month in which discrepancy is accepted, the proper officer may initiate audit under Section 65 or special audit under Section 66 or inspection, search and seizure under Section 67 or proceed to determine the tax and other dues under Section 73 or Section 74.

(ICAI FAQ PUBLICATIONS 06-09-2017 SCRUTINY OF RETURNS: FAQ NO. 12)