Australian Jon Durand sets a new world record for distance in a hang glider, beginning with a foot launch from a hillside or mountain top. This was accomplished in Australia, where it’s currently summertime, of course (you’re going to need plenty of thermals).
Try 496 kilometers in eight hours. That article is in the pilot’s own words, so is quite interesting.
The absolute distance record is 437.8 miles (704.6 km), and I believe was almost 12 hours in duration. That was done in Texas, but the launch method is by aerotow from an ultralight. That has some advantages in that the tug can search around for lift and drop you off in it, and you can begin already at several thousand feet agl. When launching from a mountain, you’ve got to hang out along the ridge until the right ride comes along, then take it.