I switched two lines in the day/night script. I've edited my post above, now it's working. Use my new edited script for increasing time, because if you just increase minutes and hours by 1 (++) like in your script, you don't have a accurate time increasing with high time speed.

I can confirm the problem with the jerking between 11 A.M. and 1 P.M.. I guess the problem is causing by precision of "var" type, maybe "double" does the job. I'll look into this and fix it.