A colleague of Brandon's named Matthew Doyle briefly consulted him on the Many Worlds theory. Matthew himself had written a script years before entitled "MANY WORLDS". 15 Till Midnight has a few varied references to this older work.
Brandon Slagle originated the general "parallel worlds" idea that he based the screenplay on when he was twelve years old.
The film is littered with Easter Eggs referencing the parallel worlds theme.
The entire storyline is a metaphor for life paths.