ST-3

yes, within 60 days now enhanced to 90 days.

Rule 7B has been inserted to allow an Assessee to submit a revised return, in Form ST-3, in triplicate, to correct a mistake or omission, within a period of 60 days from the date of submission of the return under rule 7. It has been clarified that where an assessee submits a revised return, the 'relevant date' for the purpose of recovery of service tax, if any, under section 73 of the Act shall be the date of submission of such revised return.

Whether the change in the period is to be applicable from April 1, 2008 or from the immediate effect

With immediate effect. But it is not important as the due date for filing next return is 25/04/2008.