if you attend the campus on the reporting date it would be very good as in the first week you will be provided with the schedules and you could be able to know about various functionalities of the parts of the college. but if due to some very necessary reasons if you are unable to attend the college, you may attend within 15-20 days with valid reason.

No you can't go after the date issued by the college. You must report at the time otherwise your seat will be cancelled. But their can be a alternative option as well in which you can apply for the next round of counselling and if your name comes in next round, then you can report at that time.