It could be that Rush sends files out to faculty reviewers/other members on the adcom, so how fast you can be reviewed depends on how fast your reviewers are...since they only give out interview invitations once a month (according to the website), it could take awhile to hear anything if you just missed the review deadline for the first set of interview invites...it could just be a matter of luck...of course, I have no idea if this is true or not, just speculation...