So we have a world described similar to questions and answers linked on Disclaimer, and the world manages to evolve humanoid life (simply assume that the world is sufficiently earth-like). Those humanoid life advances in a path quite similar to those two answers mentioned above. We could say that the population would grow to be quite large (say around one billion in the whole planet, spreads across the land, with land-to-sea ratio around 2/5, quite similar to earth), and their cities evenly spreads across the globe.
Assume their technology would be quite similar to 1700s-1800s and they spreads mainly from the seas (like Netherlands, Spains, Portugals), and they had colonized most of the continents.
Suddenly a meteorite (or meteorites) with large quantity of siderophiles hits one of the continents, and wipe out 2/3 of their population, especially higher ratio of death on the impact zone.
The remaining nations (especially on the other side of globe) would have to struggle through the effect of impact(s). Assume they could, and now the world is now in early new ice ages (and assume it had been years or decades, long enough for ejected dusts on the atmospheres had been dissipated). As in their early exploration (mainly ships) after the event took place (driven by curiosity and awe), they found large amounts of new materials, and heavy elements.
Building from the backgrounds:
How long would it take for them to learn about those new substances and utilize it to advance their technology up to modern-day human?
Edit 1: world population halved to make the setting to be more realistic. (As mentioned in the comment that based on our world population, around 1800s is about a billion. Also changing "1700s" to "1700-1800s", as this is a rough estimation of their tech level, not an exact equivalent (as their tech level might progress differently).