thanks sushmita for a2a.
your question is so subjective that how much time will it take to crack a banking sector exam and this can not be answer objectively that with preparation of six month you can do or not. the honest answer will be see where do you stand in the crowd. first it test you majorly on the areas like quantitative ability, logical reasoning, decision making, verbal ability which are so much innate and IQ based thing.
so firstly take some mock see where do you stand and start preparing. all the best.