When is the right time to start my coaching for MBA entrance exam now I am going b.com 2nd to 3rd year.

Usually MBA entrance exam coaching is of 1 to 2 months duration & students join it a couple of months prior to the date of the open test. The open tests normally are scheduled between Oct to Jan of a year ,so you should ideally join the said classes sometime during the 3rd year & a couple of months

Right time to start coaching is before 1 year, it is suitable time to join coaching. You can easily cover all your topics with revision a get enough time for practice.