I've checked online and have spoken to several Disney Reservation personnel, and have gotten conflicting answers to this seemingly simple question: are Disney tickets good for 14 days after their first day of use, or does the first day of use count as one of those 14 days? "The Unofficial Guide" supports the latter; however a Disney rep who has worked there for twenty years assured me that the countdown begins after the first day of use.
According to this info on Disney's website, "Magic Your Way Base Tickets expire 14 days after their first use."
So, if you first use it on say, December 1, it will expire on December 15. Are you actually going to be there for more than 14 days? If not, why worry about it? If you are, and you plan on spreading out your tickets over more than 14 days, I'd visit a guest services location at one of the parks to make sure you'll be able to use your tickets during your entire stay. Especially if you're staying on Disney property, I'm sure they'll work with you.
We were behind a family at tapstyles who lost their last day as they thought 14 days after first use meant you could enter park on day 15. NO your ticket expires at 2/3 am on day 15 to allow for entry to late evening emh. This family were refused entry and escorted away from tapstyles. So if first entry is sat your last full day will be the Friday but you will be allowed access to MK late emh after midnight on fri night/ sat morning. When system resets for sat opening tickets become invalid. Hope this helps