[jiberius]

The delay after taking long exposures is caused by the camera taking a dark frame with the same exposure length as your actual image. When you take a long exposure, the sensor can exhibit noise caused by "hot pixels". The dark frame is taken with the shutter closed so that the camera can get an image of just the hot pixel noise, which it then subtracts from your actual long exposure.

You can turn this off in the settings, but I imagine it's way easier for the camera to correct for this specific kind of noise than for Lightroom to do so.

I believe it kicks in once the exposure length is >2" on my Sony A7ii.

[tpolzer]

On the one hand that's correct. On the other hand you could completely avoid that if you did long exposures the way a Google Pixel (2+ I think) does it (in software):

Take lots of short exposures and fuse them. If the device is handheld you get variability in positioning for free, if it's on a tripod, it will automatically wiggle the OIS slightly to achieve the same effect.

[anamexis]

It seems like movement would be effective for averaging out random noise, but the described process isn’t for eliminating random noise, it’s for eliminating persistent hotter pixels on the sensor.

[IneffablePigeon]

Indeed, and in fact the pixel does exactly the same dark frame trick to identify hot pixels. I don't know that it takes as long though - perhaps it's hidden by the fact you can keep doing other things while the photo is processing.

[tpolzer]

It cannot do the same thing as an a6000, as it lacks a physical shutter.

[scrumbledober]

That's great information and makes me much less frustrated with my slow a6000.

[throwanem]

You can also try turning off long exposure NR in the menus. I don't know if it makes enough of a difference on the a6000 to be worth leaving enabled and paying the extra cost in time, but that's a way to find out.

[penagwin]

Oh thanks for letting me know! I have an A6000, so that makes sense!