Victor Salva wrote the "Every 23 years for 23 days it gets to eat" rule in El demonio (2001) so there would be no sequel unless the movie was set in the future, and he knew the studio wouldn't want that. However Francis Ford Coppola found an easy loophole: set it during the same 23 days as the first movie. So this movie is set on the 23rd day for the purpose of not making another sequel.
After the students abandon the bus and run away from the Creeper, some of the teens were to originally stumble upon an abandoned military bunker with a similar set up as the church from the first film. There, they'd stumble across the Creeper, who is in the middle of eating the dead body of an athlete. This scene was story-boarded and the set was even completely finished, but the scene was ultimately not shot.
Originally Trish and Jezelle from the first El demonio (2001) film would hunt down The Creeper for the sequel, while a school bus full of teens terrorized by The Creeper was just a subplot. But the more Victor Salva worked on the script, the more the bus plot became more interesting. So he decided to scrap Trish and Jezelle and concentrate the film on the bus instead.
The road scenes were all filmed on a small stretch of private road on the Tejon Ranch in California. Interiors on the bus were filmed on a stage in an airport hanger.
Victor Salva: (at around 49 mins) Director usually makes a cameo appearance in his movies, but because this film has no good spots for him to appear, his face can be seen very briefly on a magazine when the Creeper reaches through the roof of the bus.