Time limit

Notice u/s 142(1) can be given requiring reason for non-filing of return/ explanation for transaction without any time limit if the return is not filed within the time limit given u/s 139(1) or before the end of the assessment year.
THERE IS NO TIME LIMIT for that.

AO first issues a notice U/s 143(2) with in 6 months from the end of the financial year in which the return is furnished.