Wow, the processes really are different in each embassy.
Unfortunately, they want us to have the medical results on hand then submit the "Notice of Readiness" before they can schedule us an interview. They might schedule you in a week's time so if you haven't got your medical results yet, you will be much more delayed waiting for another date. I'm not quite sure but they said not to risk it.
What is inside packet 4? That's great that you're the ones booking your interviews though. At least you'll have an estimate date on when you can enter the US. If you show up in the interview without the medical results, would they still interview you but submit the 221g for the medical results?