Hey there! First and foremost, you need to look for references for that lighting to get a better idea of how things will be affected at that time of day. Like the ocean, the colour of the water is not completely blue but more desaturated blues, green and some oranges. I put the sun hiding behind the fortress; therefore, most of the fortress will be a bit darker because it does not get sunlight directly. Maybe some elements have a rim light, though. On the other hand, you can use the ambient light to help giving volumen to the objects, but for this, you must have in mind their form; otherwise, it will be quite hard to shade each object properly. If you find hard sculpt forms while painting, do a drawover indicating each object you want to paint. On the other hand, focus on giving more details to the most important structures; do not paint all the buildings there! Keep in mind which buildings are farther and which ones are closer to the camera, so you can have a better separation in your values and suggest atmosphere perspective. I paint a simple element in the foreground just to balance the composition. Hope this hels!
