It's an interesting idea, but I don't think it's quite compelling. Your argument assumes that God is in time in much the same way we take ourselves to be in time: experiencing only the present and acting only in the present. But, being omniscient, God would really be experiencing all times at once; and being omnipotent, he would be shaping the entire universe at once, from (temporal) beginning to (temporal) end or throughout an unbounded, infinite duration. An omniscient and omnipotent God engages in only one grand act of creation which is fully transparent to Him. Or so it might be said in response to your argument.

Still, I believe your conclusion can be supported in another way. With regard to omniscience we might ask whether God can really know why He exists. We find this question raised, for example, in a little-known passage in Immanuel Kant's masterwork The Critique of Pure Reason: "We cannot put aside, and yet also cannot endure the thought, that a being, which we represent to ourselves as supreme amongst all possible beings, should, as it were, say to itself: 'I am from eternity to eternity, and outside me there is nothing save what is through my will, but whence then am I?'"

And with regard to omnipotence we might ask analogously whether God has control over His own existence: does God exist if and only if He so chooses?

Now if we can make sense of an affirmative answer to the latter question, then we may use it to answer the first: Yes, God can know why He exists; God can know that He owes His existence to His own omnipotent will. But I cannot make sense of this idea that God's existence is due to His own decision to exist. So I agree with your conclusion that we have reason to reject the hypothesis of a literally omniscient and omnipotent God.