Is it required to do all puzzles at once when the solving for the first puzzle is initiated?

I would like to know if the offline finale round of Sudoku Mahabharat is the same as Indian Sudoku Championship? Is it the same tournament?

When you initiate the contest, the time limit of the contest starts. You have to solve all the puzzles within this time. However, note that you can submit one puzzle at a time.

The main rounds of Sudoku Mahabharat finals and Indian Sudoku Championship are largely the same. However, the aim of Sudoku Mahabharat is to encourage new solvers. From the main rounds, players who are eligible for SM playoffs move forward to compete in SM playoffs and thereby the winners of SM are decided. You can read about the eligibility of SM playoffs here.