Hii Amit!
Your question seems a little confusing. The NIOS exams for class 12th are held in two blocks. Block A is in the months of March- April. The practicals will usually be held in the morning, so you need to reach atleast 1 hour prior to the exam centre. The theory timings are 2:30pm to 5:30 pm. For more details, refer the following link -
https://www.google.com/amp/s/school.careers360.com/articles/nios-12th-date-sheet-time-table/amp
Hope this helps.
Good luck!