Other than past the file completion deadline, there is not a universal too late. There are just too many variables: nomination types, competition in the district, medical issues (yours and your competitors), 7th semester grades/changes in class rank, and repeated testing. Officially, your file is not complete until those 7th semester transcripts are in (fall college transcripts for more seasoned candidates); however, admissions will academically qualify a file based on 6th semester transcripts.
Your best best to improve your odds is to aim for completion at a reasonable early date - 1 October - then keep testing, finalize nomination packets/interviews, and update admissions after the new year.