Now your just being silly. This seems to be just a game to you. I give up I don't want to play anymore.
if you could see the whole earth from a high mountain, and the earth is flat, then you could certainly see the sun 24 hours a day and there's no such thing as night time.
let's wait a few hours and see if nightfall happens, then.
if it does, it is not possible the earth is not flat.
if it is light outside 24/7, the earth is possibly flat.
simple, right?