Arminian Kerrigan Skelly states that he is not an Open Theist for a few Biblical reasons. He quotes Revelation 6:
Rev 6:9 When He opened the fifth seal, I saw under the altar the souls of those who had been slain for the word of God and for the testimony which they held.
Rev 6:10 And they cried with a loud voice, saying, “How long, O Lord, holy and true, until You judge and avenge our blood on those who dwell on the earth?”
Rev 6:11 Then a white robe was given to each of them; and it was said to them that they should rest a little while longer, until both the number of their fellow servants and their brethren, who would be killed as they were, was completed.
Skelly then states his objection to Open Theism:
How can God know with certainty exactly how many are going to be killed or that any more at all will be killed when killing a Christian for being a Christian is a freewill decision… not only that but how does God know there will be any more martyrs at all period because for all He knows all people who have a chance at being a martyred could depart from the faith and choose not to be martyrs and deny Christ and there would be no more martyrs at all.
When Calvinists debate against Open Theists, they naturally assume that if Open Theists say God does not control everything then the Open Theist is claiming that God can do nothing. Likewise, Arminian Skelly assumes that if Open Theists claim God does not know the future then God cannot predict the actions of free will agents.
Because future human actions are largely predictable by almost anyone, Skelly’s claim is wildly unfounded. It does not take a rocket scientist to predict that if we drive to Walmart right now, the clerk will accept cash in exchange for any candy bar we pick out. Even very dull human beings can accurately predict unknown future behavior of other human beings. That someone does not even have to know the cashier personally to know this future freewill decision. If humans can this easily and accurately predict other human behavior, how much more-so can God with access to infinitely more resources?
The verse in question does not quite suggest what Skelly believes it suggests. It appears that in the scenario, God is waiting until a certain magnitude of Christians are killed. The scenario suggests that God is not waiting for Christian number 31,732 to die, but God is waiting for a certain rough tipping point to enhance the impending vengeance.
It is very important to note that no time-frames are given, only rough estimates. How long? A little while longer. If God had the future locked in His mind, God could have provided a more definite answer. But God does not talk like someone who has the future mapped out in minute detail in His mind. Instead God speaks as if He has plans and then works with human actions to accomplish His purpose. In other words, the entire story of the Bible from God’s cascading series of contingency plans with Pharaoh to the crucifixion of Jesus.