CA course is of 4 5 years and to persue this course you have to clear CA foundation exam which can be given right after your 12th exams. From next year , you can appear for CA exam in May right after your 12th exams are finished.

For this you have to make sure that you register yourself for this course. And only registration is not enough you have to fill application form of CA foundation exam in order to inform ICAI that you are going to appear for this exam.

Earlier , CA foundation exams were used to held in November after competion of 12th board so students used to get enough time to prepare for this exam but from the next year it will be held twice in a year first in May and second in November, students willing to appear in May month exam has to start their preparation during 12th itself but if you are thinking to appear for November attempt then you have enough time to prepare for this.

But according to me , appearing in May month exam is the best because it saves your time but it's totally upto you in what way you are comfortable.

Hope this information is helpful.

Thank you