You can actually do an MBA whenever you want. It will simply help you to move up the career ladder. If you have worked as a CA for more than 3 years then you can also go for the executive MBA program which is for 1 year only. Just try to manage your time a little to prepare for the management entrance exams and get a good college that offers an executive MBA program and you'll be good to go. It will help you in your growth.

All the very best