Christina,
Thanks for asking your question to planDisney!
I think you have it exactly right. Since you are staying at
Disney's Old Key West Resort, you will be able to take advantage of the
Extended Evening Theme Park Hours. These are a fantastic way to get more time in the parks. With the lighter crowds you get to ride more attractions and experience more of the ambiance.
However, you do have to have been in that park prior to the extra hours to enjoy them. That would mean you either had that specific park selected as your initial park of the day, via the
Disney Park Pass system, or you had the Park Hopper option on your ticket and you had made your way over to that particular park earlier that afternoon. Remember that with park hopping, it is subject to availability at the second park.
It sounds to me, based on your question, like you are in the first group and will want to make sure that your theme park reservations are booked for those particular parks on those specific days.
At the time of this answer, I see Extended Evening Hours posted on the
Walt Disney World Calendar for parks through May 17, so you are likely just days away from seeing them posted for the dates of your vacation. I would suggest that you go ahead now and make your theme park reservations. When they post the extended hours for the dates of your trip you can consider what changes you might want to make to your schedule.
BONUS TIPI just checked the
Disney Park Pass Availability Calendar, and based on your arrival date it looks like all four parks are available for you to pick your theme park reservations. Don't wait around too long to pick them!
Write me back if you have any follow-up questions.
Have a Magical Vacation!
Doug