Suppose wishes don't fail and all simulacra are created in a neat line (so that they can pass the rod) in a likewise infinite plane, sequentially but within the 6-second turn.

Also suppose (I'm not too confident that there's any time in between the spell being cast and having an effect) that it is possible to take a free item-drop action before being planeshifted away, and that letting go the fork before the spell has any effect does not ruin the spell.

You get infinite simulacra in the Abyss at the same time, each occupying their own spot in space, but only a finite number of them can actually be in range of any specific demon, unless they have no volume.

This finite number is not large enough to guarantee that they manage to kill their target demon. They might all miss.

Suppose wishes don't fail and all simulacra are created in a neat line (so that they can pass the fork) in a likewise infinite plane, sequentially but within the 6-second turn.

Also suppose (I'm not too confident that there's any time in between the spell being cast and having an effect) that it is possible to take a free item-drop action before being planeshifted away, and that letting go the fork before the spell has any effect does not ruin the spell.

You get infinite simulacra in the Abyss at the same time, each occupying their own spot in space, but only a finite number of them can actually be in range of any specific demon, unless they have no volume.

This finite number is not large enough to guarantee that they manage to kill their target demon. They might all miss.