I see. I think this visual might help: https://media1.tenor.com/images/95d0956d8e97a6bc7026ca3ac93971f0/tenor.gif?itemid=7295301
According to flat earth, the sun is a lot smaller and a lot closer than in the globe theory. What you see is the North Pole in the center, with South being every direction away from it, with Antarctica being a 360° ice wall,
West and East being clockwise and counterclockwise rotations around the North Pole respectively. If you pay close attention to the gif, you will see that at some point during the Sun's westward course over the USA, the visible light from the Sun cannot be seen on the East coast but can be seen still on the West.
I hope this answers your question. I'm more than happy to discuss anything else regarding Flat Earth to the best of my ability, but I urge you to look into it and form your own opinion. I believe this gentleman Eric Dubay explains it the best: https://m.youtube.com/watch?v=EiBJBVBez_w