Sky atmosphere day/night cycle problem

Hi, i have a project where Im using sky atmosphere for simulate the lighting in a tropical beach, i want record a video in sequencer where the sun sets and a moon rises making the stars appear.
I watch this video: Exploring the depths of the new Sky & Atmosphere system | Unreal Engine - YouTube, here it is shown that it is possible to add the stars when the sun sets but I don’t understand how the material is created on purpose and how it is used to mask.
does anyone know how I can investigate the matter? or if there is another way?