It is recommended, but not necessary.
The latest I recommend you take your DAT is 1 month AFTER application opens (this will cause your application to be considered late). You want to take it months in advance before application opens so your scores will be ready when AADSAS opens. Ideally, as a traditional applicant, you would want to spend time studying for the DAT when you're not in school (so summer)
example:
June 2015 - Study for DAT
August 2015 - Take DAT
Sep 2015 - May 2016 - Retake DAT/Do well in school
June 2016 - Submit DAT to AADSAS
As a non-trad, you're time is more flexible. However, I would still recommend taking it 4 months in advance of June 201x. To retake the DAT, you need to wait 90 days.