UPS will occasionally reschedule, it depends. If the tracking information says that it was received by UPS already and then your date changed, that's probably a UPS problem. If the date has remained the same since you got the tracking info, then it could be a problem at the Eden warehouse or with UPS pickup time or with any number of unforeseeable circumstances.
It also depends on where you live and whether or not you got your delivery dates before or after inputting your zip code.
You can call UPS and find out why they rescheduled, too, if you've got the tracking number