The trial period for the additional night time hours does not begin until May 9th and then runs to May 22nd.
Here is the info from the DIS home page
E-Night Trial Period Planned for 2004
There's a special treat in store for guests staying at a onsite Disney resort from 5/9/04 to 5/22/04.
Plans are in the works for scheduling eight Extra Magic Hour Evenings. Guests staying at a Disney resort will be able to enjoy select attractions at the designated theme park for up to three hours after the park closes to the general public.
Wristbands will be given to guests producing a valid Key To The World Card. They will be distributed beginning three hours prior to the start of the the event. (Guests staying at the Swan/Dolphin or the Lake Buena Vista Hilton are eligible to participate. ) Guests staying at Shades of Green will be eligible for only the morning Extra Magic Hour.
Regular park admission will be required. Guests using single day passes cannot "hop" to the selected theme park offering the evening hours, but must have used their pass for that park on the day of the offer.
The Extra Magic Hour morning schedule will remain in place. The attractions open in the evening can vary from those running during the morning.
The schedule for the Extra Magic Hour Evenings is:
Sunday - Epcot
Tuesday - Disney-MGM Studios
Wednesday - Magic Kingdom
Thursday - Animal Kingdom
Fastpass will be available.