When there's no more room in hell, the dead will walk the earth.
Following an ever-growing epidemic of zombies that have risen from the dead, two Philadelphia S.W.A.T. team members, a traffic reporter, and his television executive girlfriend seek refuge in a secluded shopping mall.
Dr. Foster explains "its been three weeks" since the outbreak, setting this film 3 weeks after an outbreak (that most assume is Night of the Living Dead). Flyboy explains that Fran is 3.5 to 4 months pregnant. Filming began on November 13th, 1977, and Christmas items are evident throughout the mall, beginning the film around the Christmas season. Somewhere in the film is a calendar with a year 197x, setting the film in the 70s.
Mar, 1978
Fran remains pregnant for a few months, but never gives birth in the movie, spanning the film no more than 5 months. The calendar Fran marks (towards the end of the film) has no month listed, but a Friday the 31st is listed. Valid dates for this would be January/October 1975, December 1976, March 1978, and August 1979. With Fran 3-4 months pregnant in the beginning (Christmas season), and not yet ready to birth by the ending, March of 1978 is the only fitting date, as it sets her around 7 to 8 months pregnant.