hi ,

A very gud morning to u. yeah you can give JEE main,but after diploma only.now you can't give  such a exams.dont worry,you're having enough time to prepare.

after diploma completion also you're eligibile to write JEE main for get qualifying for JEE advance to enter into IIT's(to the first year) only not will be considered as lateral entry.you cant get NIT admission.

all the best!!!!!!! 

 please refer this link for your reference:   https://engineering.careers360.com/exams/jee-main

I Hope this information will be useful to you.

if you need additional information,let us know to help you.

Thank you!!!:)