Revision of income

If any person having furnished a return under section 139(1) or in pursuance of a notice issued under section 142(1), discovers any omission or any wrong statement therein, he may furnish a revised return at any time before the expiry of one year from the end of the relevant assessment year or before completion of assessment, whichever is earlier.
It may be noted that a belated return cannot be revised. It has been held in Kumar Jagdish Chandra Sinha v. CIT [1996] 86 Taxman 122 (SC) that only a return furnished under section 139(1) or in pursuance of a notice under section 142(1) can be revised. A belated return furnished under section 139(4), therefore, cannot be revised.
So, in this case, you can revise the return on or before 31.03.2013 or before the completion of assessment, whichever is earlier.

The processing of the return does not tantamount to assessment.  Only if the assessment under sec 143(3) is done, you cannot revise the return.

If Intimitaion and refund is received u/s 143(1) you can always revise the return nevertheless the return being processed.

Hence, you can revise the return u/s 139(5) on or before 31.03.2012