Does creation ex nihilo determine which possible world is actual?

The usual Leibnizian idea is that, prior to creation, God surveyed all the possible worlds, and actualized one of them. Assume that God is a temporal being, and that God's actions are temporal. Consider an arbitrary time t which is prior to creation ex nihilo and at which God is engaged in surveying the possible worlds.

Question: is there an actual world at time t?

If the answer is No, this would seem to entail that God's activity at t is occurring in every possible world. On this basis, one might be inclined to think that there is exactly one and only one possible world at time t (which, paradoxically, would suggest further that there is an actual world at time t). Maybe there are infinitely many worlds at time t which share an identical temporal segment; Plantinga probably dissusses this, I'll have to go back and look.

One way to think about God's situation at t might be this: at time t, every possible past is identical, but there are infinitely many possible futures. So, maybe God's activity at time t isn't so much that God is surveying possible worlds, but possible futures.

One way to spell things out, then, would be this. At time t, there are infinitely many possible pasts that are identical. At time t, there are infinitely many distinct possible futures. God's activity at time t is actual, i.e., belongs to the actual world, which is one of infinitely many identical pasts. At time t, it is indeed open to God to determine which world is actual -- which future becomes distinct from the infinitely many identical pasts -- even though God's activity at time t is actual (i.e., belongs to the actual world).