Based on the source, it doesn't look good.
var today = new Date();
That is always going to be the user's system date.
If you absolutely must fix this, look down a line; you could override $.datepicker._daylightSavingAdjust and return the date from your server *
But this is a bad idea. Why on earth do your users have their system date so messed up? Why is that your problem? If they complain, tell them to fix their clocks.
* I can't emphasize how bad an idea this is. That function is used to normalize most of the dates in the datepicker, so you'll have to write some pretty convoluted logic to keep from messing everything up. That may not even be feasible.
