["Holy Terra"? Sure she's heard of Earth called Terra and obviously Wicca promotes the worship of the planet in a way, but that's not something she's ever heard.]
I'm guessing you've never seen that time travel movie with Michael J. Fox and the DeLorean in it, huh?
Well, say every time you make a choice, there's multiple futures at any given point, always being generated. This could be anything so minor as pancakes vs. waffles one morning or major as an assassination or invention or so on. Little changes can change things a bit and major things change things a lot.
Now factoring in everyone making those kinds of decisions, or maybe the laws of physics are a little different from the start, and you get countless universes all running parallel to each other. Each of these has its own timeline.
The prison warden has pretty sophisticated systems - it can pull people here from any point in those timelines. I happen to be from the planet Earth in the year 2004 A.D., but there are people here from different Earths, different planets completely, or different times on my Earth.