It isn't God's job to manage the Devil for us. It is ours.
James 4:6-10 (KJV)
6 But he giveth more grace. Wherefore he saith, God resisteth the proud, but giveth grace unto the humble.
7 Submit yourselves therefore to God. Resist the devil, and he will flee from you.
8 Draw nigh to God, and he will draw nigh to you. Cleanse your hands, ye sinners; and purify your hearts, ye double minded.
9 Be afflicted, and mourn, and weep: let your laughter be turned to mourning, and your joy to heaviness.
10 Humble yourselves in the sight of the Lord, and he shall lift you up.
Where in Genesis, the time slot for Job, did God teach Job or even Abraham such a principle? That is peculiar to the Church. There is no discussion in Genesis of matters of faith, what to do about fear for Job to learn by way of a patriarch to know the role of faith concerning fear. We have fear of man by animals, fear of God, men fearing men, and individual encounters with God saying not to fear. Where does God say fear is a sin?
Job knew 'the boys' were partying, which in itself was not described as sinful, but maybe you are thinking Job was concerned mostly over the boys having the girls over eating and drinking? That combination might have been of concern given they were not constrained by the Law of Moses. At no point did God indicate Job was in sinful fear for his children. He performed similar sacrifices as by Jewish priests centuries later who did those because people sinned and needed intercession, whether a particular individual was a friend of God and clean or failed. They did that by commandment from God. The priests didn't sacrifice out of fear that someone sinned.
So why would it be a sin for Job to do that, not willing to just let it go hoping they turned out in good standing with God? We as parents have spent the last 35+ years praying for our children from before they were born, our reasonable sacrifice. For that matter, I don't recall Abel's sacrifice being of fear, but was well accepted of God. The concept of obedience was the rule in Genesis, that of Abraham accounted as godly faith, well explained in the New Testament, but not the Hebrew Bible. It took the NT to explain adequately what that faith of Abraham was about, and is for us. But who else contemporary with Abraham had to do with faith? What I do find is fear and sacrifice. Abraham gave up Sarah in Egypt to the king out of recognition those people had no fear of God. It took a dream for that ruler to release her to Abraham untouched, God regarding the integrity of his heart in the matter.
Abraham's proved willingness to sacrifice Isaac while there was no lamb they hoped for was counted as "fearing God", not called faith then. We could at best define the old concept of faith as fearing God. Even after Israel had witnessed the miracles of their deliverance, God found them later in Deuteronomy as faithless, but were fearing God.
I'm thinking over your "I don't know why you say, 'but God said instead'. satan didn't ask to kill Job, though I'm sure he would have like to. he asked God to put forth His hand and afflict Job and he will curse you. God said, go ahead, but don't kill him. (Job 2:5-6".) Satan wanted God to do the deed, while God said it was in Satan's hand, only not to kill Job. Looking at the Hebrew there is no command from God to touch Job. He let Satan do it. God lets people and angels do lots of horrible things, not often having a hand directly in them except to write with His finger twice. When His hand was involved He commanded angels and men to do things like commanding Joshua to kill every human in Ai, keep the spoils, then burn it down.
God simply ignored Satan's request, issuing His own command to let Satan do the deed. I believe He could do that fairly without darkness, knowing the outcome before it happened.
