Multiple days were common in the old versions to get good lighting and atmosphere.

In 6 Infinite, I just had one go about 60 hours with just a sky, clouds and water. I was testing a new sky with some new clouds I'd worked up and a new water material. I wanted to once and for all see what Vue would do, so I set all the sliders to ridiculous.

The sky came out awesome with the graininess gone and the most realistic clouds I've managed but the price in time was high. I would not do it except to print a still as a poster.