Hello, Katherine! Welcome to the Disney Parks Moms Panel. Let's use the Force to find out how you can plan for all the great special events at Walt Disney World Resort.
Dates and details on special events tend to be announced a few months in advance. The very best way to keep up on event announcements, dates, pricing and other info is to follow the Disney Parks Blog. You can check out this post from December that announced the dates that Star Wars Weekends would be coming in for a landing at Disney's Hollywood Studios for 2015 (May 15 - June 14, by the way!).
I haven't yet seen an official announcement about Harambe Nights returning to Disney's Animal Kingdom this year, but last year's Disney Parks Blog post with the event dates came out on May 2, 2014.
There is a page on the Walt Disney World website that lists all tours and events that happen throughout the year. It's a good place to see a general description of all of the events in one place.
Hope this helps you navigate to your favorite events, Katherine. Please stop by again if we can help you plan your visit.
Have a magical day!
Kathy K.