This discussion clarifies the deadline for investing in Notified Capital Gain bonds to claim exemption under Section 54EC. For sales made on 4th January 2020, the investment deadline was extended to 30th September 2020, or before filing your tax return for FY 2019-20, whichever came first. This extension was formally announced via Notification No. 35/2020.
In your case you can purchase Notified Capital Gain bond to claim exemption u/s 54EC up to 30th day of September, 2020 or before filing your return u/s 139 (due date 30th November 2020) for F.Y 2019-20, whichever is earlier.
Date for Investment under section 54EC is extended to 30th September, 2020 via Notification No.35 /2020/ F. No. 370142/23/2020-TPL dated. 24th June, 2020