The first application you will fill for any entrance examination will be of JEE Mains in the month of september 2019  and for another attempt the registration will start in month of february 2020.
The registration for other engineering  entrance exams will start in the month of February that includes BITS,VIT ,KIET and various other entrance exams.
But be attentive as some exams are only for particular state candidates. Hence you may not be eligible for those exams.

Dear student, 

The application forms for various entrance exams for engineering will start releasing from nov 2019 up to march-may 2020.

There are number of exams such us jee Maine and advance, bitsat, viteee, gate, srmjee, state jee's, nata and lot more so you need to be alert from the month of November for getting the application process done within the time. 

Hope it's been helpful to you.