Application for Commutation of pension should be submitted to the HO not later than three months before the date of Superannuation. No such application shall be entertained if the period is less than three months from the date of superannuation of the Government servant

Central Civil Services (Commutation of Pension) Second Amendment Rules, 2014(Please click the link below)
http://ccis.nic.in/WriteReadData/CircularPortal/D3/D03ppw/Notification_355_E_260514.pdf