First off - congrats on getting to the interview stage!
As for the nominations that you might have read about, that was a part of the old process before the change a year or two ago. Instead of nominations, you now get placed 'Under Consideration' prior to your interview. After the interview, you will either get an invitation, be placed on the waitlist, or just told that you weren't selected. This happens at any time from now until the very last moment of the know-by date (one of those annoying 'it depends' type PC-situations).
In my current group, we had people that received their invitation the same day, and others who literally waited three months (interviewed early, but were notified late).
Also, as a clarification, under the old system, the recruiters did the interviews and 'nominated' you to the placement officers. Nowadays, you actually interview with the placement officers themselves and the recruiters don't have much to do with the process once you submit your application.