The question is why/when do you want your MBA? would you prefer working on your start-up? Lets say you work on your start-up and it takes off. Your MBA gets pushed out a couple of years. is that fine by you? If it is, i'd say go for the start-up. If the MBA is more important to you, then re-take. IIT+670 will put you on the low-end of the scale.
I graduated from IIT kharagpur and its been 4 years working in oil industry. I have also started a venture of my own. My concern is that the score which I have is considerably less to aim something very high.Its just 670 so should I go for a retest or focus on the start-up which I can possibly convert into a working entity by the start of the 2nd round..Your inputs will be helpful.