They're pretty good about not jerking you along. They send people home in the middle of the interview if they failed something. If you make it through the day, you have a pretty good chance of getting hired.
I interviewed mid-June and got the Fed-Ex eight days later. It really depends upon when the next class is and how close it is to full. People getting the invitation same day still happens, but only when they are close to the next class start and an opening exists. A class just started on the 28th, so the earliest another would start is probably the 19th. I have noticed a fall-off in the number of interviewees this week, for whatever that is worth.