NTA hasn't officially released the dates for April session of JEE Mains. The possible reason why it might not be conducted iin the last week of April is that the current lock down will end by April 15th. And there might be students who have opted for exam centres far away from their places. They might have to travel and the circumstances wouldnt be so welcoming because April 15th is not the day when Corona virus will leave India. It is a lockdown period for preventing the transfer of the virus through community transmission. So at this point in time May has been selected assuming that the virus can be prevented from being spread. JEE Advanced might be pushed to June/July of April Session is postponed to May. Please watch out for the official information.