< Hank Hill voice > I miss voting for that man < / Hank Hill voice >
The tunnel goes to an alternate version of Earth, 80 million years ago. They had not control over where it went and when, just found it. No danger of changing the past as they aren’t in their own past, so to speak.
I think they just found a wormhole. They didn't get to pick what year they go back to.
The show is just okay. I like stuff with dinosaurs, but the whole premise about how mankind ruined the earth is typical liberal gibberish. If you listen to their description of how the camp runs, it also sounds like they've tried to create a socialist utopia.