Eligibility Date for Vat Credit

Hey

Can Anyone tell me what is the date on which a dealer becomes eligible for vat set off

(Question relating to Maharashtra VAT)

Eg: Related to Vat Audit

Assume You Have Vat Payable in Month of April as per determination

But in month of May It comes Excess Set Off

Till What Date Interest for The month of April is To be calculated

1)21/05/2008 to 01/06/2008 or

2)21/05/2008 to 21/06/2008)