It depends on the school. I would imagine that some make decisions as their cycle progresses while others sit back and examine the pool and cherry pick students. I do know that some schools, such as Case, mention the benefits of applying (and presumably interviewing) early. If a school has extended an invitation for you to interview with them then that is indeed a very good sign that they are taking you and your application seriously. Focus on making a great first impression and less so on the date. Best of luck!