So... based on the demons response here... do we think they know the future... or they have just read and accept God’s prophecy? Just curious...
And it came to pass, as we went to prayer, a certain damsel possessed with a spirit of divination met us, which brought her masters much gain by soothsaying: / The same followed Paul and us, and cried, saying, These men are the servants of the most high God, which shew unto us the way of salvation. / And this did she many days. But Paul, being grieved, turned and said to the spirit, I command thee in the name of Jesus Christ to come out of her. And he came out the same hour. / And when her masters saw that the hope of their gains was gone, they caught Paul and Silas, and drew them into the marketplace unto the rulers, / And brought them to the magistrates, saying, These men, being Jews, do exceedingly trouble our city, / And teach customs, which are not lawful for us to receive, neither to observe, being Romans. …
— Acts 16:16-21
I think they just know the prophecy and know it is true. Remember, demons used to be angels, so they would have had knowledge of God far more directly than we do. Satan could quote the Bible verse for verse when he tempted Jesus in the wilderness, too.
Now, their behavior may seem strange, but we do all sorts of inexplicable things too, when we are under the influence of our sinful natures. Also, they probably know that they have no chance of redemption at this point, so their is no “carrot” to entice them to behave.
Eternity exists before, during, and after, what we perceive as time/space.
It's a difficult concept to grasp. Our limited perception is a big mental block. The fish don't know they are in a fishbowl. Just because you can't see it doesn't mean it doesn't/didn't/always exist.