I.E, if my key is set to expire next Wednesday, can I still use it Wednesday until the park closes that day, or is it expired the second it becomes Wednesday at 12:01AM?
You’ll still be good to go on Wednesday! Your key will be valid until the park closes that day, so you can use it all day, even if it technically expires at midnight. It’s the same as when your hotel check-out is on the last day of your stay—you can enjoy everything until the end of the day!
They are good for 365 days. Add a leap day into the mix and things get complicated. Your best bet is to see if you can make a reservation. If you can then you are good to go.