I'm Just a Girl Who Can't Say D'oh - S30-E20
Trivia: Ned Flanders inspired the creation of an Arizona-based metal band called Okilly Dokilly, whose members all dress like him. They appeared in the end credits of the season 30 episode I'm Just a Girl Who Can't Say D'oh.





Answer: I'm not sure if this is the one you're thinking of, but an episode of "Ray Bradbury Theatre," called "A Sound of Thunder," dealt with a similar matter: a group of hunters travel back in time to hunt dinosaurs, only to find things have changed when they get back because someone stepped on a butterfly.
Xofer