 According to "the lost tape", which contains gun shop owner Andys  personal video diary (accessible as a bonus feature on the  directors cut DVD), the main characters arrive at the mall early in  the movie on May the 9th. Therefore, the movie opens a day earlier  on May the 8th (Andy mentions that attacks on citizens by the undead  had already started on the 7th). Andy makes his last entry just  before he turns into one of the undead on June the 6th, and the  movie ends on that same day (not including the footage during the  end credits). This places the events of Dawn of the Dead in a space  of just 29 days