They no longer open early, they used to allow you in to stroll down Main Street, etc, but they have started doing the "Welcome Show" which is in front of the Train Station on the turnstile side. Unless you have a priority seating for breakfast you will be held in front until the park is officially opened by the characters. AK also has a morning show, so they are similar in this aspect (not sure about MGM)
At the end of the night however the stores will remain open past park closing time (usually about an hour or so) so you can stay later in the park, but you can not get in earlier without a Priority seating.
