Hello,
You only get two consecutive attempts at JEE Advanced. First attempt is just after you pass in your class 12 and the second attempt is a year after you pass class 12.
For JEE Mains, you get three consecutive attempts in three years. In a year, you get two attempts at JEE Mains, one in January and in April.

So , If you have just passed your class 12, so you can take admission into Bsc course and prepare for JEE Mains and JEE Advanced as well.
But it would be really a hard process. You need to focus both on your Bsc studies as well as JEE preparation. You can also take a year drop and prepare for JEE Advanced.
So think wisely.
Please visit this link JEE Advanced preparation strategy

Please visit this link for JEE Advanced eligibility criteria
Hope it helps

IIT Madras

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