Take a look at the engine content sky sphere material.
The exact name is: M_Sky_Panning_Clouds(2) (Not sure if I accidentally duplicated it once or not… so it might be without the two. Yay for “testing” projects that are supposed to be temporary but aren’t in the end!).
It’s setup in a way that allows a dynamic transition between night and day based on a float spanning between -1 and 1 which is mapping to color values on curves that in the end drive the time of day.
The BP in question exists as part of the engine content.
Color curves are an asset type that you can create and replace the default engine curves with your own to create your own style with the preexisting skybox.