Omniscience and Free Will

Was creating time the result of a decision God made? If so, how could he decide to create time before creating it, if 'before' didn't exist, since there was no time?

Metaphysically, God must exist outside of time, outside of all things. If there is anything above God or more infinite or eternal than He, then He is not God, for there is something greater. God must be the eternal creator of ALL things, including time, else he is not God, by definition. And even if He were somehow still a creator of things except time, He would be a liar, for he has said he is creator of all things. But since we know God cannot be a liar since God is good and goodness, and lying is objectively sinful, then He must be telling truth, and He must exist outside of time.
Next note the language of Genesis 1:1, where it says "In the beginning God created the heaven and the earth" implying that before the beginning, God already was. Therefore God must exist at least before time, but what is before time except outside of time entirely. And if He is outside of time, it must be that He is free to move about time, but since God does not much but everywhere always, it must be that He is in all periods of time.
These aren't really presuppositions, these seem to just be the fundamentals of what God is and must be.

I don't know. I already said before that thinking about outside of time (or before, if you like) is practically impossible, it's thinking outside a dimension we don't comprehend.

Attached: first way.jpg (700x6826, 560.17K)

Time proceeds from God, and God is in it the same way as logic proceeds from God and he's in accordance with it.

Being in accordance with something isn't the same as being subject to it. It means He sets the standard.

Pretty much this. I personally hink of it as a non-linear view of time/something beyond human comprehension, like with Abraham and Sodom.

Does this mean God's prophecies can be potentially wrong?

Of course not. God knows all possibilities AND the actual outcome of all things.