Let me put this theory out there ... I'm going to Reader's Digest this, because I'm going to assume some concepts that are themselves their own thread.
satan went back and forth between this world and and God's eternity. Job is an example, I believe there are others but for brevity let's just assume that satan has/had access to both the eternal, and from there any point in time.
And there are arguments to be made that those angels who 'fell' with satan had that same access, able to, from the eternal, access any point in time and go to and fro.
Now, again, this is it's own thread, but understanding that access to any point in time is key to the next step. Imagine a wheel, the hub is eternity and time is the rim. That means God in eternity/the hub can reach out to any point on the rim/timeline, like inserting a spoke. So He puts a spoke to the top of the rim, then one to the bottom. One to the left, and one to the right. One kitty corner this way, one ktty corner another way. So when we're talking of access to time from eternity, we're understanding that that access is random and not constrained to our chronology. Meaning, a demon can move from July 1 2018 into the eternal, and being in the hub can then re-enter time July 28 2018. Or November 16 1843.
And true