Nothing is impossible. But practically, it is much harder to crack CLAT in just 40 days. But yes, if you are desperate towards your studies, then you can definitely crack it in just 40 days. To crack and to grab a seat in one of the top 5 NLUs, you need to word harder and harder. If you give your complete 40 days (without wasting a single minute) to it with proper dedication, then you can grab a seat in one of the top 5 NLUs.

Hope it helps.