If you ask me, I would recommend following the suggestion I received (described in this thread) :
"Wait for the interview to be scheduled. If treatment is not completed, send evidence of ongoing treatment and request an extension based on the anticipated timeline. It will likely be granted, and you will be rescheduled."
In your case, send evidence of the expected results date (e.g., the exam receipt or information from the website—anything proving you have completed the exam and that the results will be available after the interview date). Then, request an extension.
Hope this helps, and I wish you good luck!