It depends on the individual as a whole. I would anyhow suggest that you begin to learn your courses before two months minimum of your targeted time. To cite that I assume the learner will join the college in June, I would recommend him/her to pursue the course from April onwards. This is the right time because the expertness in the linguistic scenario will never be familiar in a short time. We need to use these skills regularly till we become master level. So, in short, it would be advised to begin your journey as possible. 

To put it in a nutshell, everyone has some concerns before joini