According to Jac Delhi official website the registration process of Jac Delhi will starts after the declaration of final results of JEE Main 2020.
You can check this notification on its website :- https://jacdelhi.nic.in/publicinfo/public/home.aspx#
Want to know more about the registration process and JAC Delhi checkout Career360 article:- https://engineering.careers360.com/articles/jac-delhi
And don't forget to check out the Career360 College Predictor to know your college admission chances based on your JEE Main Rank, Home State, Caste, Gender, etc. - https://engineering.careers360.com/jee-main-college-predictor