Hey I am a D3 at Maryland.
Submit BEFORE retaking your DAT. While your application is not considered complete without the new DAT scores, it will create a folder so you are reviewed once your scores are finalized and verified (plan on 4-6 weeks later). Your 18 may meet the minimum at some schools. You can always email or call letting adcom at the school know as well, and it obviously will show up on your aadsas application