Creation myths in Micronesia speak of human spirits (differentiated from the soul) being forged by a volcano god, using heat and a hammer. They had no metal on the islands, but understood the basics of forging. so Im assuming it was at the very least 2000 BP (the second migration), though it could be before 4000 BP, when they first arrived on the islands.
They considered the Volcano god to be the devil, and the volcano led to hell, so they are pretty much hells angels.
For clarification; are you asking about Micronesians or Austronesians?
Austronesians (though better to say Austronesian speakers since the 'Austronesians' aren't so much a people as they are a culture) are spread all across the Pacific (near/remote Oceania; or Micronesian/Polynesia/much of Melanesia); as well as island Southeast Asia and all the way to Madagascar off the East African coast.
According to Environmental Historian Peter Boomgaard (whose Frontier of Fear is definitely worth picking up if you ever wondered about Human/Tiger history in SEA); the earliest evidence of metal working in SEA and therefor among Austronesian peoples was between 500- 200 BCE, which would have been after the initial peopling of Micronesia and the Polynesian heartland (Tonga-Fiji-Samoa). Matt Matsuda and Boomgaard both see metalworking in the Malay-Austronesian world as arriving through the long distance trading networks that already ran between South and East Asia at this time-- carrying not just metalworking to the western end of the Austronesian world, but also ideas such as Buddhism and Sanskrit.
I am not familiar with the Micronesian legend of which you write. Perhaps you could be more specific as to the island it comes from? I would definitely be curious to find out more. The ones of which I am most familiar begin with five spirits arising from a fresh water well; one, a bachelor, heads off finding humans and creating a half human- half spirit people, most of which settle on Guåhan (Guam). In these stories the islands of the Eastern Carolines and Marianas were all the domain of spirits until the half humans and humans began to come. No where in this series of stories about spirits, humans, and magic clams, is there anything about forging-- though fire does appear in the stories concerning the creation of pottery.
Having a 'hell' or 'devil' in the story certainly leads me to wonder if it is not a more recent (recent as in sometime in the past 250+ years) syncretic retelling of a traditional story in light of Christianization-- syncretism being a common outcome of cultural mixing/adaption and well documents across Oceania for example. Many of the Tahitian myths with which I am more familiar have obvious biblical references and parallels thanks to evangelical missionisation at the beginning of the nineteenth century. This is especially clear when concepts like Po or night become synonymous for the underworld and Ao or light/world becomes the equivalent of Heaven.
As you say in your question; there were no metals to be found in Micronesia and therefor no metalworking. There is precious little metal to be found in the Pacific in general- with notable exceptions in New Caledonia/Kanaky, Fiji, Papua New Guinea, and the Solomon Islands. Though none of the metals there were necessarily available before modern processing techniques and so metalworking was unknown in the island Pacific; but was available in island Southeast Asia. And just to speculate-- because we know that the island Pacific/SEA are only divided by our own arbitrary division and that there were in fact connections between them; that especially between the Philippines and the Eastern Carolines/Marianas (Palau for sure), it is possible that worked metal may have made it to the islands through trade. Though this is entirely conjecture since there is precious little evidence from those more distant time periods much less extensive material evidence.
Good overview of Pacific history and connecting together the entire Austronesian speaking world.
One possible collection of myths from the Micronesian cultural region.