From 16 hours, to 16 minutes, in that one single step.
This is just the default final render node settings of the .tgd you uploaded, I'd say no longer than 30-45 minutes at the size 800x550px, that you have posted above. Maybe an idea to quickly run through all the quality settings before commiting to a final render that will tie up your computer for hours and hours unnecessarily.
A cloud 'quality' of '1'(full quality) is usually adequate.
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* The line in your terrain comes from the Perlin billows noise in the fractal terrain. Also, the orange colour doesn't need checked in that fractal as it won't appear in the render. The terrain shaders before the 'compute terrain' node only supply displacement information to the scene, colour is applied after the compute terrain node. Unless you plan to use the colour output of that shader to feed another shader function further down the chain then it doesn't need checked at all. And, if you do need to do that at any point, black and white would be your best bet for choice of colours as it will give you the correct control(contrast/roughness/etc) of the range between black and white.
