Hi Elizabeth!
Thank you for bringing your question to the Disney Parks Moms Panel. While I purchased my Annual Pass directly at the park, I know several friends that have purchased months in advance to help with budgeting for their future trips!
There is an activation time period that you'll have to pick up your
Annual Pass on property, but since it's currently set as December 31, 2030, I think you'll find yourself able to pick them up
long before the expiration date! It sounds like your plan to purchase in May or June and activate at Walt Disney World Resort during your fall trip will work out
practically perfect. To activate upon arrival, please visit any Walt Disney World Resort theme park ticket window or Guest Relations location. They'll get you set and ready to go in a jiffy!
I hope this helps in planning your future visits. Please come back if we can help in any other way!
-Lindsey