For this year i.e. Jee Main January Session 2020, the application form was released on 3rd September, 2019 and the last date to fill the application was October 10, 2019. Every year, around this time application for Jee Main January session started. But this year it's bit different. Jee Main April 2020 session in now going on and the session 2020-21 has not yet started. And due to this pandemic the situation is not in our hands. So it is really unpredictable when the Applications will be released and when will be the exam. Jee main 2021 schedule hasn't yet released. As of now we don't have the information if this exam of next year will be postponed or not. Jee Main January application usually starts in the month of September and April session starts in the month of February. You can start checking the official website, for any kind of updates and if the application releases it will be updated there. There might be a delay in the application of Jee 2021 as most of the events of 2020 have been delayed.
http://news.careers360.com/expect-slight-delay-in-jee-main-2021-january-exam-dates-prof-ramgopal-rao-director-iitd