Selecting day / night mode

Hi
I am creating a game, and i want to select day / night mode before the game starts.

Anybody knows how to do this, I have an idea and want to share.

I make a mission file without the sun, and this is for night mode, if day is selected, then i add the sun dynamically and add it to the MissionCleanup. Is this a good idea? Will it work for me or not?

Please provide your suggestions

Thanks