What registration are you referring to
The Neet 2019 exam will be held on 5th may 2019
the results will be declared by 5th June 2019 and verification process will occur in the latter part of June with the different rounds of counselling being held in the month of July and the beginning of the session will possibly be from mid August as usual
if you are talking about the MBBS registration of the new batch of 2019 MBBS first year students than that can only occur after the students have been allotted the final colleges and that takes place by around September to November and you will be notified about it on your respective health university websites