Mostly CAT preparation takes 6 months-1 year for students with general aptitude.
But with students having a high aptitude, 2 hours a day in 6 months is enough time for practice, especially if the student belongs to good graduate school. As because of this, his /her basics would be clear.
However, it will depend on what your goal is, or what your score needs to be. It could be anywhere from 5 months to 12 months.
Preparation time also depends on the :
Urgency of giving the test.
However there is no alternative of practice. Practice, practice, practice until you get a very high CAT score. There are various books and online programs that can help you to achieve this goal along with self – study, hard work and determination.
Like most exams, good study material, a study plan, a group of friends for group-study, some coaching, all are required. However, due to CAT being one of the older MBA entrance exams, a lot of the study material is outdated. Then again, if you have even somewhat above average vocabulary, then spending weeks learning a list of words and their synonyms shall be a very bad investment. But several students spend weeks, often months learning synonyms. (This might make sense for the GRE, but will yield poorly for CAT). Also, one needs to ensure that one indeed understood a particular question and topic before proceeding. Too often, students are satisfied simply by getting the right answer. The idea is to focus on the right approach and speed building."