Yes , ofcourse it would be a very good time to start your praparation for clat exam .Since you have not started preparing for it from your 11th class that dosen't matter.Now , you have only 5 months till your preboards starts for your basic work of clat which you have to place it accordingly for the best preparation with more intensity as less months are left , the 1 month after boards could be your revesion month. So , make sure to make very elaborative and detailed notes which would be easy to revise in that last month of revesion process.

hope you do good in your clat exam .

all the best!