Section 96A(1)(a) in The Central Goods and Services Tax Rules, 2017
(a)fifteen days after the expiry of three months or [such further period as may be allowed by the Commissioner,] [Inserted by Notification No. G.S.R. 1304(E), dated 18.10.2017 (w.e.f. 19.6.2017).] from the date of issue of the invoice for export, if the goods are not exported out of India; or