At http://disneyworld.disney.go.com/planning-guides/in-depth-advice/extended-theme-park-hours/ it says
Each day, one of the 4 Walt Disney World theme parks opens one hour early or remains open up to 3 hours after regular closing time.
Is the days for each park published anywhere? I had no luck searching myself but I'm not sure where to look.
Here is the schedule for the rest of 2012, which I got from here. It was apparently compiled from Disney's calendar pages. According to the page you linked to, "Upon check-in at a Walt Disney World Resort hotel, Guests will receive a schedule detailing when each park offers Extra Magic Hours" so if any last minute changes have occurred, that will be the most accurate. But the information below should allow you to start planning.
July 2012
Morning Extra Magic Hours
Magic Kingdom - July 5, 12, 19, 26
Epcot - July 6, 13, 20, 27
Disney's Hollywood Studios - July 7, 14, 21, 28
Animal Kingdom - July 2, 4, 9, 11, 16, 18, 23, 25, 30
Blizzard Beach - July 5, 12, 19, 26
Typhoon Lagoon - July 4, 11, 18, 25
Evening Extra Magic Hours
Magic Kingdom - July 3, 6, 8, 13, 15, 20, 27, 29
Epcot - July 1, 10, 17, 24
Disney's Hollywood Studios - July 2, 9, 16, 23, 30
Animal Kingdom - No Evening Extra Magic Hours
Blizzard Beach - No Evening Extra Magic Hours
Typhoon Lagoon - No Evening Extra Magic Hours
August 2012
Morning Extra Magic Hours
Magic Kingdom - August 2, 9, 16, 23, 30
Epcot - August 3, 10, 17, 24, 31
Disney's Hollywood Studios - August 4, 11, 18, 25
Animal Kingdom - August 1, 6, 8, 13, 15, 20, 22, 27, 29
Blizzard Beach - August 2, 9, 16, 23
Typhoon Lagoon - August 1, 8, 15, 22
Evening Extra Magic Hours
Magic Kingdom - August 3, 5, 10, 12, 17, 19, 24, 26
Epcot - August 7, 14, 21, 28
Disney's Hollywood Studios - August 6, 13, 20, 27
Animal Kingdom - No Evening Extra Magic Hours
Blizzard Beach - No Evening Extra Magic Hours
Typhoon Lagoon - No Evening Extra Magic Hours
September 2012
Morning Extra Magic Hours
Magic Kingdom - September 6, 13, 20, 27
Epcot - September 4, 11, 18, 25
Disney's Hollywood Studios - September 1, 8, 15, 22, 28
Animal Kingdom - September 3, 5, 10, 14, 17, 21, 24, 29
Evening Extra Magic Hours
Magic Kingdom - September 2, 9, 16, 23
Epcot - September 7, 12, 19, 26
Disney's Hollywood Studios - September 3, 10, 17, 24
Animal Kingdom - No Evening Extra Magic Hours
October 2012
Morning Extra Magic Hours
Magic Kingdom - October 4, 11, 18, 25
Epcot - October 2, 9, 16, 23, 30
Disney's Hollywood Studios - October 6, 13, 20, 27
Animal Kingdom - October 1, 5, 8, 12, 15, 19, 22, 26, 28
Evening Extra Magic Hours
Magic Kingdom - October 1, 7, 15, 22
Epcot - October 3, 10, 17, 24, 31
Disney's Hollywood Studios - October 8, 14, 21, 29
Animal Kingdom - No Evening Extra Magic Hours
November 2012
Morning Extra Magic Hours
Magic Kingdom - November 1, 8, 15, 22, 29
Epcot - November 6, 13, 20, 27
Disney's Hollywood Studios - November 3, 10, 17, 24
Animal Kingdom - November 2, 4, 9, 12, 14, 19, 21, 26, 28
Evening Extra Magic Hours
Magic Kingdom - November 10, 11, 18, 26
Epcot - November 7, 16, 23, 30
Disney's Hollywood Studios - November 5, 12, 19, 25
Animal Kingdom - No Evening Extra Magic Hours
December 2012
Morning Extra Magic Hours
Magic Kingdom - December 6, 13, 20, 23, 24, 25, 26, 27, 28, 29, 30, 31
Epcot - December 4, 11, 18, 23
Disney's Hollywood Studios - December 1, 8, 15, 22, 24
Animal Kingdom - December 3, 5, 10, 12, 17, 19, 25, 28, 29, 30, 31
Evening Extra Magic Hours
Magic Kingdom - December 3, 10, 17, 23, 28, 30
Epcot - December 7, 14, 21, 25, 27
Disney's Hollywood Studios - December 2, 9, 16, 26, 29, 31
Animal Kingdom - No Evening Extra Magic Hours
