Due date for revise tax invoice as per st

Sir under service tax there is no due date mentioned for revising tax invoice. You have to issue invoice first time within 30 days(45 days for banks,NBFCs etc.) after completion of service or receipt of payment, whichever is later, under Rule 4A. After that if u have to revise invoice then you may revise invoice as many time as you want. This is my interpretation.