it took us a little over 2 months.
we brought the same documents that greencard brought. we laso brought medical results but i don't think they really need it. if oyu have a lawyer, better asked them coz it's just a waste of money to take those medical exams.
by the way, our interview was held at LA. in our case, most of the questions asked were about employment. we were not able to get an approval because we failed to bring one document (current ITR of the company). then the office told us to wait for 6 months. we're still waiting...
i wish you the best in your interview...