The end-Permian mass extinction was very fast by geological standards

[lpetrich]

The Earth has had several mass extinctions over its history, with the best-known one being the K-T/K-Pg one at the end of the Cretaceous period. That was the extinction that killed off all the (non-avian) dinosaurs. But the P-Tr one, the one at the end of the Permian, was even bigger, even if it did not involve everybody's favorite extinct animals.

Boom, they all died -- PZ Myers, Pharyngula
End-Permian extinction, which wiped out most of Earth's species, was instantaneous in geological time (2018)
End-Permian extinction happened in 60,000 years—much faster than earlier estimates, study says (2014)
Timeline of a mass extinction: New evidence points to rapid collapse of Earth’s species 252 million years ago (2011)
sudden end-Permian mass extinction in South China | GSA Bulletin | GeoScienceWorld (2018)
High-precision timeline for Earth’s most severe extinction | PNAS (2014)
Calibrating the End-Permian Mass Extinction | Science (2011)

From the 2011 phys.org article:

While the causes of this global catastrophe are unknown, an MIT-led team of researchers has now established that the end-Permian extinction was extremely rapid, triggering massive die-outs both in the oceans and on land in less than 20,000 years — the blink of an eye in geologic time. The researchers also found that this time period coincides with a massive buildup of atmospheric carbon dioxide, which likely triggered the simultaneous collapse of species in the oceans and on land.

With further calculations, the group found that the average rate at which carbon dioxide entered the atmosphere during the end-Permian extinction was slightly below today’s rate of carbon dioxide release into the atmosphere due to fossil fuel emissions. Over tens of thousands of years, increases in atmospheric carbon dioxide during the Permian period likely triggered severe global warming, accelerating species extinctions.

The researchers also discovered evidence of simultaneous and widespread wildfires that may have added to end-Permian global warming, triggering what they deem “catastrophic” soil erosion and making environments extremely arid and inhospitable.

From the 2014 phys.org article:

Now researchers at MIT have determined that the end-Permian extinction occurred over 60,000 years, give or take 48,000 years—practically instantaneous, from a geologic perspective. The new timescale is based on more precise dating techniques, and indicates that the most severe extinction in history may have happened more than 10 times faster than scientists had previously thought.

"We've got the extinction nailed in absolute time and duration," says Sam Bowring, the Robert R. Shrock Professor of Earth and Planetary Sciences at MIT. "How do you kill 96 percent of everything that lived in the oceans in tens of thousands of years? It could be that an exceptional extinction requires an exceptional explanation."

In addition to establishing the extinction's duration, Bowring, graduate student Seth Burgess, and a colleague from the Nanjing Institute of Geology and Paleontology also found that, 10,000 years before the die-off, the oceans experienced a pulse of light carbon, which likely reflects a massive addition of carbon dioxide to the atmosphere. This dramatic change may have led to widespread ocean acidification and increased sea temperatures by 10 degrees Celsius or more, killing the majority of sea life.

A common theory is that this CO2 was emitted by the Siberian Traps eruptions, eruptions that had created big lava plains there.

From the 2018 phys.org article:

The new study, published today in the GSA Bulletin, reports that in the approximately 30,000 years leading up to the end-Permian extinction, there is no geologic evidence of species starting to die out. The researchers also found no signs of any big swings in ocean temperature or dramatic fluxes of carbon dioxide in the atmosphere. When ocean and land species did die out, they did so en masse, over a period that was geologically instantaneous.

... From their analysis, they were able to determine that the end-Permian extinction occurred suddenly, around 252 million years ago, give or take 31,000 years.

...
For example, the researchers found signs that the ocean temperature rose from 30 to 35 degrees Celsius from the base to the top of the 27-meter interval—a period that encompasses about 30,000 years before the main extinction event. This temperature swing, however, is not very significant compared with a much larger heat-up that took place after most species already had died out.

"Big changes in temperature come right after the extinction, when the ocean gets really hot and uncomfortable," Ramezani says. "So we can rule out that ocean temperature was a driver of the extinction.

... But according to the team's new data from the Penglaitan section, even though increased global volcanic activity dominated the last 400,000 years of the Permian, it doesn't appear that there were any dramatic die-outs of marine species or any significant changes in ocean temperature and atmospheric carbon in the 30,000 years leading up to the main extinction.

This 20,000 - 30,000 years is an upper limit. Did it happen even faster than that?