Dear aspirant !

Hope you are doing great ! There is no particular date of admission ,may be you don't know the whole admission process in btech , firstly you have to give jee mains for nit ,iiit etc and then jee advanced for IITs.  You can get admission in private colleges without these exams but there you have to pay a heavy amount of money . Now it depend on you in which college or university you want to take admission , check the particular site of that college time to time for application form ,but for IITs and nits the admission for 2022 will be after jee advanced and mains respectively.

For jee mains 2022 ,visit the link given below ;-

https://www.google.com/url?sa=t&source=web&rct=j&url=https://engineering.careers360.com/articles/jee-main-2022/amp&ved=2ahUKEwiP5OPz9sr2AhW1zTgGHW8bCl0QFnoECAUQBQ&usg=AOvVaw0MK_nHUuH-7yTGxus_3sLb .

Hope it helps you !

Thank you