I have created a tutorial on how to implement day and night cycle in unreal. posting it here because someone might find this useful.
I have created another blueprint by extending the skysphere blueprint and the M_Sky_Panning_Clouds material is modified to add a moon as well.
Time of day system : Unreal Time of Day - UE4 Open World Tutorials #21 - YouTube
Adding Moon to sky sphere : Unreal Moon with SkySphere Material - UE4 Open World Tutorials #22 - YouTube
Moon phases : Unreal Moon Phases - UE4 Open World Tutorials #23 - YouTube
Lighting based on time of day : Unreal Time based Dynamic Lighting - UE4 Open World Tutorials #24 - YouTube
