there was a very long wait before i got interviewed. i arried at 10:15 am, and got in the embassy without waiting online.
but i was the second last to get interviewed i think. so when i got out of the embassy, it was already almost 2pm. very bored and anxious.
so i would suggest to go earlier, since they are basicly not following the time given anyway.
btw i had a 15 days AP after my oral approval at the interview. 7 days in Immigrant visa application AP and 7 days in Non-immigrant AP.
this was quite a frustrating waiting, glad i did not buy ticket too early. so warning here, an oral approval does not gurantee anything. wait your case to become "issued" then make any plans.