Trivia: The book Evan gets his instructions from (Ark Building For Dummies) is an actual book which has been published! Mainly as a joke.
Trivia: There are multiple scenes in the movie showing the ark being built, and standing on land waiting for the flood. All of these shots of the ark before the flood was a real, life-size ark, built for this movie.
Trivia: The scene where God appears in the backseat of Evan's car and they are both visible in the rear view mirror, is reminiscent of the movie poster for "Driving Miss Daisy", also starring Morgan Freeman, where Freeman and Jessica Tandy were both visible in the rear view mirror.
Trivia: There are several biblical mentions in this movie if you look (The 40 Year Old Virgin Mary, Eve Adams, etc.).
Trivia: 'The 40 Year Old Virgin Mary' is a reference to Steve Carrell's previous role in 'The 40 Year Old Virgin'.
Answer: The Biblical new year began on the autumnal equinox, which falls on or around that date. The ancient Hebrews strove to get all their work done before the end of the year, to prepare for the High Holy Days that followed.