Changing skyboxes?

Hi, i wanted to implement a day and night system in my game, but i also wanted to have a skybox, so that the sky didn't look like one plain color. So would a simple way to go about this be just scripting something to make the fog get gradually denser and darker, simulating a day and night effect? Or could i use a similar system to swap between like 7 different skyboxes, which would look like different times of the day? If there is, is there a way to make them fade gradually, so it isn't obvious that the texures are just being swapper? Thank you so much, I realize that this maybe a novice question.