dear yashwanth,

No it is not mandatory to report at the exact time of reporting given in the admit card but remember that it is mandatory to reach at the test centre before the closing time of gate mentioned in the admit card.

But in my opinion you should reach at the the reporting time mentioned on the admit card because in online exams there is many verification process that you have to pass through and it will take more time and at the exam centre there is a huge crowd of candidate .