I'm not sure where I read this, so it may not be very credible, but I read that Case interviews very few people at a time. They stretch their interviews out over a longer period than most schools, and gradually fill their class throughout Spring, rather than filling most of the class in December. If this is true, it makes perfect sense that there would still be a good chance you'll get accepted from an April interview. Last stat I saw said they accepted (approximately) 260 out of 280 interviewed. So, it shouldn't make a whole lot of difference when you interview, since getting an early interview doesn't seem to provide much benefit (unless all 20 of those not accepted were after March or something, which I cannot comment on). If you get an interview, you'll have a great chance of being accepted.