In a previous question I wrote about a javascript date function that was mysteriously stopping on 11/07/101. Thanks to the stackoverflow users I was told my problem is Dayl
Use Date.setHours(hour,min,sec,millisec) to set the hour default to noon:
Date.setHours(11); (view reference)
24 hours after noon on a day is guaranteed to be the next day, though on daylight savings time days it will be one hour off (which doesn't change the result in your script at all).