What are the Production render settings for animations?

[KushKush]

Thanks for pointing out the issue, hopefully, it will reduce render time.

[KushKush]

KushKush I think your step size is way too small. Here is the description of the parameter from the docs:

Step size – Determines the size of one step through the volume. Smaller steps produce more accurate results but are slower to render. In general, dense volumes require smaller step sizes than more transparent volumes. In practice, step sizes that are two to three times smaller than the Fog distance parameter work well.

Usually setting it to 1/4th or 1/5th of the distance has worked well for us (250m-200m in your case)

Does step size parameter changes with the unit scale? Is it is, is there a difference in render times when the scene is at different unit scales?

[^Lele^]

All you need to care for is the ratio between the distance and the step size, regardless of which units they're expressed in.
You were forcing the fog to be sampled to its max steps (where, ofc, the max distance was visible) per pixel sample (so, multiplicative with the AA), which are clamped (bottom of the dialog) to 1000, by default.
That's bound to take a long time.
Check the log often for clues as to what's taking the most rays, you'll then know where such a problem may lay.
Using a samplerate RE will further narrow down the areas that are sucking up AA samples.

[^Lele^]

As for the dark line at the edge, try lowering the horizon line (by raising the horizon offset value in your vraySun/vraySky -if it overrides the sun node-).

[KushKush]

Check the log often for clues as to what's taking the most rays, you'll then know where such a problem may lay.
Using a samplerate RE will further narrow down the areas that are sucking up AA samples.

What is simplerate RE?

[fixeighted]

https://docs.chaos.com/display/VMAX/VRaySampleRate

[KushKush]

I was meant what RE stands for, I assume its render, Thanks Fixeighted.

[fixeighted]

Oh...lol...it means Render Element

[^Lele^]

As fixeighted said: Render Element
In other engines' lingo, they are also called AoV (arbitrary output values), but they are very much analogous.

They are added from the aptly named render settings tab (the last one).