What makes some meteor showers continue for days, while the "Unicorn shower" can be shorter than one hour? The Washington Post's One hundred meteors in 15 minutes? ‘Short-lived outburst’ of shooting stars forecast for Thursday night. says:

A “short-lived outburst” is forecast for Thursday evening around 11:50 p.m. Eastern.

and later:

The prediction of an outburst comes from NASA research scientist Peter Jenniskens and Finnish Fireball Network’s Esko Lyytinen and was published in MeteorNews. The pair specialize in sniffing out meteor outbursts and storms, expertly calculating the orbits of various celestial bodies that give rise to meteor showers. Scientists still haven’t pinned down the object depositing the debris anticipated to trigger this display.
However, outbursts in 1925, 1935, 1985 and 1995 offered enough information for the team to produce a model. It indicates the close passage of a dense pocket of spaceborne debris. That narrow but potent debris stream is likely to manifest in a 15-to-40-minute-long barrage of meteors around 11:50 p.m. Eastern on Thursday, according to the researchers.
What will it look like? Jenniskens and Lyytinen indicate events in 1985 and 1995 produced 700 and 400 meteors per hour and wrote that this event could emit anywhere from around 100 per hour to even more than 1,000 per hour, the latter considered a meteor “storm.”
The outburst is calculated to last a fraction of an hour, so those numbers can be sliced in half. And because the radiant point of the meteors will be comparatively low in the sky, we can trim off a bit more.

The linked Meteor News article LIKELY ALPHA MONOCEROTIDS (AMO#246) OUTBURST ON THE MORNING OF NOVEMBER 22, 2019 gives orbital elements derived by different groups of astronomers that can be used to predict the time of maximum.
But what is it that makes this debris trail so narrow that the shower is predicted to last less than one hour while other showers can sometimes extend for several days?
It sounds like this effect:


  ... in addition to the usual shower on August 12th, there might be an extra surge of meteors on August 11th caused by a filament of dust newly drifting across Earth's orbit.
  The filament, like all the rest of the dust in the Perseid cloud, comes from Comet Swift-Tuttle. The difference is, the filament is relatively young. It boiled off the comet during the Civil War, in 1862. Other dust in the cloud is older (perhaps thousands of years old), more dispersed, and responsible for the month-long shower that peaks on August 12th. The filament will eventually disperse, too, but for now it retains some of its original ribbon-shape.


The 2004 Perseid Meteor Shower NASA