Here's to some speculation because I have nothing better to do. I get the feeling that Yale might be sending out invites to the rock stars, strong indicators of high performance such as grades, GMAT scores, cured cancer, brought peace to the Middle East etc.
I suspect "average" applicants will start seeing invites a bit later, once the AdCom has had a chance to go over the 'qualitative' aspects of the application package.
Average in quotes because, let's face it, you are applying to Yale because you think you deserve to be there. So, you've probably done something worthwhile, yeah?