time limit

1.If the person on whom a notice under section 148 is to be served is a person treated as the agent of a non-resident under section 163 and the assessment, reassessment or recomputation to be made in pursuance of the notice is to be made on him as the agent of such non-resident, the notice shall not be issued after the expiry of a period of six years3 from the end of the relevant assessment year.
2.The CBDT has issued Instruction No. 5/2017 dated 7th July 2017 by which it has laid down the procedure and criteria for compulsory manual selection of returns/cases requiring scrutiny during the financial-year 2017-2018. It is also stated that cases are also being selected under CASS-2017 (Computer Aided Scrutiny Selection) on the basis of broad based selection filters and in a non-discretionary manner in two categories of Limited Scrutiny & Complete Scrutiny.
3.After receiving the Directions in the nature of guidance from DRP the AO shall, in conformity with the directions, complete the assessment without providing any further opportunity of being heard to the assessee, within one month from the end of the month in which such direction is received.
4. u/s 254- within 4 years from the date of the order, 
u/s 263- 2 years from the end of the financial year in which order sought to be revised was passed. 
u/s 264- within 1 year from the end of financial year in which such application u/s 264 is made by the assesee.