Hello Prabhat,

In most of the colleges, the regular classes don't start after the given date of commencement, there are things like an introduction and orientations happening in the first week of college. But it is not the scenario of all the colleges, some colleges start the classes from the first day. If you for any reason don't attend the classes for the first week the basics of all the subjects will be lost but you can easily cover that by yourself.

All The Best.