Hello Samantha,
Thanks for stopping by planDisney with your question. You are just days away from joining
The World's Most Magical Celebration!
Adding the
Park Hopper Option to your tickets will give you the flexibility of visiting multiple parks in the same day. In fact, I have known people who have visited all 4 parks in a single day just to experience their favorite attractions!
Although you could add the Park Hopper Option to your tickets on the last day of your vacation, you'll be purchasing the upgrade for the entire length of your ticket. So, if you had a five day admission ticket, you'll be adding the Park Hopper to ALL five days, even though you only have one day left to visit the parks. For this reason, if park hopping is something you really want to do, you may want to add it now and try to work it into your entire vacation.
I know we love spend our mornings in one park and then "hop" to
EPCOT in the evenings to enjoy whatever festival is going on and finish up our night watching
Harmonious. Similarly, we like to start our day in
Disney's Animal Kingdom, take an afternoon break to escape the heat, and then hop over to
Magic Kingdom to end our day with classic attractions and
Disney Enchantment.
While there is no way to guarantee that the park you plan to hop to won't reach capacity, it's unlikely. Except for during extremely busy times, guests are typically able to head to any other park at 2:00 PM (or whenever park hopping starts), even if there were no morning reservations available.
Hope this helps. Have a magical vacation!
Diane