Appointment was at 9:30. Tried showing up at 8:30 but was told we were "too early" and to come back at 9:00.
Pleasant surprise was that I as the petitioner was allowed to accompany my parents (applicants). Emails and websites made it sound like applicants would be on their own.
After arriving it was a 2.5 hour wait to get to our number. First stop was "pre-screening" which involved handing over a bunch of documents. Just a few basic questions like addresses. Documents that we prepared but were NOT required included: petitioner passport and proof of domicile and IRS transcript (though this was asked for later). Total time for both parents was about 20 mins.
From there, we went back to waiting for the actual interview which came up in about another 20 mins. The interview was also a breeze, with more fingerprints being taken and ask for the IRS transcript. Several original documents were given back (except for passports) and approval was granted! Questions were once again very basic.