For claiming exemption under S. 54B and 54F it is not necessary that investment should have been made within original due date of filing return under S. 139(1), even belated return u/s 139(4) is also eligible for exemption .
PCIT v. Shankar Lal Saini. (2018) 253 Taxman 308/ 168 DTR 226 (Raj)(HC)
S. 54F : Capital gains – Investment in a residential house -Relief is available if unutilized sale consideration in capital gain account scheme within due date of filing belated tax return under S. 139(4) [ S.45 , 54B ]