Canon GAFT limits itself to human history on Earth. This is not a fixed boundary, but more of a general assumption. It is far, far easier to create compelling adventures when you have other people around to bounce off of. You can only run from dinosaurs for so long and have it still be amusing.
There is no reason the cast can't travel to other planets except ... how many worlds do you want to build? If the answer is lots - there are a lot out there to make up. Meanwhile, there's plenty to do on Earth.
When concocting this Fantastical History, we went with flexibility, trying to accommodate as many myuths, trops and common assumptions abut the future as we could. A fair bit of thought and research went into this (no - really) but where sources conflicted, we went with the most interesting.
We try to stay within known facts about history and science because we already laying a heavy burden of disbelief right from the premise. Even so, don't let the actual facts bog down the story. If you can't find what you want in actual history, just make it up and move on. History is wrong a lot anyway. This is not historical simulation. It is a cartoon simulation. Try to find the flavor of the place without letting all the research dry it out.
Even so, homo sapiens, as a recognizable species, has been around for at least a million years, and human beings, as a distinct variant, have been around for at least 100000 years, and yet we only have about 6000 years of recorded history. And the future, of course, is completely undiscovered. So there is ample space for fabrication.
GAFT canon stipulates that the present, right now, is about in the middle of the human experience on planet Earth. So we have loosely charted 100000 years in either direction.