I believe the day/night cycle, and the opening/closing months actually have no effect in-game, they don't change profits or anything. I think it does change how fast the "night" starts and ends, though.I remember someone mentioning once before the only thing opening times did was determine whether or not you had a night/day cycle. I can't confirm that though.
I feel like when I was playing I never had a night cycle, but it's been so long I forget if I'm correct on that or not xD
EDIT: If that is true though then you could maybe set your opening hours for night time only and you'd never have daylight...?