IIM interview panelists like candidates who are good at time management, people who could make time for CAT preparation during their busy schedules. But all this matters if and only if, you score a high enough percentile. Only people who get called for IIM interviews have the chance to start justifying the gap year. My best advice to you would be to try to score a very high percentile, because no matter how many Nobel prizes you win in the coming year, unless you score a high percentile, it won't be enough.

its not necessary but in the elite colleges you can expect questions related to gaps during your personal interview and it also plays a role in your admission process as well