From the site;
The Lockheed Martin X-35 was chosen over the competing Boeing X-32 primarily because of Lockheed's lift-fan STOVL design, which proved superior to the Boeing vectored-thrust approach. The lift fan, which is powered by the aircraft engine via a clutched driveshaft, was technically challenging but DoD concluded that Lockheed has the technology in hand. The lift fan has significant excess power which could be critical given the weight gain that all fighter aircraft experience.

I wonder if the Lockheed lift-fan design will overcome the current Harrier's short hover duration due to overheating of the engines. The current design allows for about 2 minutes of water to control heating during hovering maneuvers if needed.

I remember seeing Harrier's hover for what seemed longer than 2 minutes so I suspect the duration of hovering depends on the conditions.

SteveS