Welcome to planDisney!
If you've often dreamed of a far-off place where a hero's welcome will be waiting for you, Walt Disney World Resort is the place for you. If you "go the distance" and cross that ocean, Mickey and his pals will be waiting and ready to give you a hug.
Having grown up in the UK, I can tell you that Guests traveling from your side of the pond cannot purchase 1-Day tickets through the
official Walt Disney Travel Company website. As you mentioned in your question, you can purchase either a
7-Day Magic Ticket or a 14-Day Magic Ticket. Both of these options give you unlimited access to all
four theme parks and the
two water parks, plus the
Park Hopper Option,
Memory Maker, and more! I'm originally from Liverpool and back in the day, I would purchase the 14-Day Magic Ticket and have the time of my life. It's a fantastic deal (and I miss taking advantage of it now I live in the U.S.A.).
However, if you'd like to only visit for one day, you'll need to purchase your ticket when you arrive in the States. You'll then be able to access
Disneyworld.Disney.go.com to purchase from any of the ticket options currently available there. Alternatively, you can even purchase your ticket once you arrive at Walt Disney World Resort. Tickets can be purchased from the ticket booths at the theme park entrances or even the
Disney Ticket Center at Disney Springs. If you purchase the Park Hopper Option, you'll be able to visit multiple parks in one day. You'll visit your first theme park and then after 2:00 PM, you'll be able to hop to another theme park of your choice. Just be aware that there are currently capacity limits at the theme parks, I'd recommend checking out the
Theme Park Reservation Availability calendar before you purchase any tickets.
I hope that's helpful! Thanks for stopping by planDisney.
Mike