I saw a movie on Syfi maybe 8-10 years ago where people were able to travel back in time to the age of the dinosaurs. They had to stay on this bridge type thing and not step off or touch anything to avoid a butterfly effect. Someone stepped off and killed a bug, and when they got back to their own time, the timeline started changing. Anyone know the name of the movie?
Unique to this adaptation of the story (different from the short story and the previous adaptation for The Ray Bradbury Theater) is that the timeline changes don't immediately manifest when the adventurers return, but propogate uptime in waves, which seems to match what you describe.
There is a brief plot description (in contrast to Wikipedia's ridiculously detailed one) on IMDb:
When a scientist sent back to the prehistoric era strays off the path he causes a chain of events that alters history in disastrous ways.