What is the time limit for making the assessment under section 143(3) i.e. scrutiny assessment?

​As per section 153, the time limit for making assessment under section 143(3) is:-

1. Within 21 months from the end of the assessment year in which the income was first assessable. [For assessment year 2017-18 or before]
2. 18 months from the end of the assessment year in which the income was first assessable. [for assessment year 2018-19]
3. 12 months from the end of the assessment year in which the income was first assessable [Assessment year 2019-20 and onwards]

Note: If reference is made to TPO, the period available for assessment shall be extended by 12 months