I tried using this verse in the open theism thread.
An “observer of times” is a witch, wizard, sorcerer, etc. that claims to be able to predict the future.
If you believe that Satan perverts everything, then we have to assume the following:
God can predict the future with 100% accuracy because He has perfect foreknowledge. Satan cannot predict the future with 100% accuracy, but he makes some good guesses due to his superior intelligence, which enables him to lure unbelievers and foolish believers.
Now, if open theism is correct, and everyone was an open theist, then we would laugh at anyone who would claim to know the future. We would say if God does not know the future, a witch surely does not know the future.
So, because God does know the future, Satan can pretend to also know the future. If God does not know the future, Satan would have nothing to counterfeit.
God knows the past and present perfectly. He can make accurate predictions about some of the future (even insurance guys and weathermen do the same to a lesser extent).
Fortune tellers, witches, etc. can guess at the future or influence it to happen at times. This is a counterfeit and pales to the infinite God, just as the counterfeit plagues could not keep up with God. These guys are deceivers and have a terrible track record guessing at the future.
In contrast, God is able to predict much of the future based on His ability to make it come to pass in some areas (nothing to do with simple or exhaustive foreknowledge, prescience, crystal ball, etc.) see Isaiah 46 and 48 for this principle.
God knows some of the future and much of it as possible. The scope of this is much greater than man or Satan (not even in the same league). It still does not prove EDF.