Walt Disney World
When checking the Extra Magic Hours go to each day and scroll all the way to the bottom of the page on that day. If you see AM that means that the theme park listed will open (1) hour earlier than posted opening time. If you see PM (2) that means that that theme park will remain open (2) hours after listed closing time. Extra Magic Hours are only for on site Walt Disney World Guests staying at a Walt Disney World Resort Property.
Keep in mind there are also After Hours Events which are specialty ticketed events. So you would need to purchase a ticket for those. One example is Villians After Dark which on average is around $145 per person currently.