This is from the Air Force site:
Step 2 Board Scores.
Beginning 2004, it is mandatory that all 4 th year students take the clinical knowledge portion of Step 2 no later than 15 September. All students will be required to submit Step 2 results before the Joint Service Graduate Medical Education Selection Board (JSGMESB). The clinical skills portion of the boards is not required before the selection board, but will be required prior to students being eligible to sit for Step 3.
Yes, that does state no later than Sept 15th!