Interest is payable only when taxable person fails to pay gst on or before the due date of filing of return. No question of interest when u have more itc then gst payable ..simply utilise the gst to pay output tax.
Interest is only payable when payment of tax is made after due date. If ITC credit is more than GST payable then if return is filled successfully on timely and set off tax liablity with ITC then no interest will be payable