There never is a nighttime that I know of, unless there's a trainer out there that will do it for you (I don't use trainers). I think it would be really neat to have some sort of night arrangement, even if it has to just be certain levels that are played only at night. You'd be able to choose the lights for the coaster, how the lights operate, their colors, things like that, and you could sell glow-in-the-dark things as well. But those are more dreams for another version of the game!
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Po!nt of View: A different look at Roller Coasters.
http://www.crosswinds.net/~justmayntz/thrills/