You can do USH in literally 4 hours. Get there when it opens, you'll be done by mid-afternoon. Then go back to DLR til midnight.
And don't skip all the "clones"! Definitely do our Pirates, Splash, Space, and Haunted Mansion. Our Space Mountain is badass.
The absolute must-do's: Indy, RSR, Pirates, Space, Haunted, Matterhorn.