That's only the first few weeks of opening. And it's open until 7 p.m. From mid May through June both parks will stay open until 9 p.m.
Use the Disneyland Resort monthly calendar to plan your next vacation and find out what's happening when at the theme parks.
disneyland.disney.go.com
Another reason why I'm not rushing to go. I want to wait to go when you get more time in the parks. And 9-9 are good hours. It's not until midnight but since there aren't any night time shows and lowered capacity in general it's probably more than enough time to do what you want, as long as you are there from the start.
And who knows, they might extend the hours a bit if they can add more capacity after June 15th.