The Central Government vide Notification no. 30/2018 dated July 30, 2018 has fixed the last date for filing return in Form GSTR-6, return to be filed by Input Service Distributor, for the month of July, 2017 to August, 2018 at September 30, 2018.
Read more at: http://www.cbic.gov.in/resources//htdocs-cbec/gst/Notification-30-2018-central_tax-English.pdf