It's usually pretty similar to regional events on Thursday and Friday - you'll see ~3 sets of technical judges, a set or two of team/outreach judges, and potentially some Chairman's judges if you're competing for Chairman's. If you see judges on Saturday, it means that you're in the running for an award, so congrats
However, there have been some instances of 'elite' teams seeing judges who aren't judging them, but who are just curious about the team. Teams can get pretty worked up about this, but don't worry too much - you'll get judged fairly.
EDIT: in response to what Katie said, what she's seen can definitely be true on Saturday and sometimes Friday, but all teams get an initial pass from the judges on Thursday or Friday.