IND AS applicability

IndAS 101 will give you guidelines on first time adoption: https://mca.gov.in/Ministry/pdf/INDAS101.pdf

converging within a two months, feb & mar, is not possible. But you can adopt IndAS even by the end of the year but needs meticulous recording. So converge from next year. 

Yes, it is mandatory from the same year the moment it is 250 crores  or above turnover.

In the above link, it states, changes should start from interim reports. I did not go through it completely, but if your are in the fourth interim, you might have to make policy changes to the other three quarters. Please check it otherwise.