Studying for the CBSE is essentially studying for the medical school Step 1.
There is an incredible amount of information out there on how to study for this test, but the general meta today is using some combination Anki (AnKing/Lightyear, etc.), UFAP (UWorld, First Aid, Pathoma), Boards and Beyond, and NBME’s for practice.
There are many more resources out there, but it’s best to do your own research and compile resources based on how you personally study, as there are a variety of ways to accomplish the same end goal, which is to basically memorize everything in First Aid.
I would wait until at least after the fall semester of D1 to start studying. The best time to take it is probably either Feb of D2, or summer before D3, but this will be school dependent.