The one I listed has a duration of 4 hours per the article. It stayed aloft for only 10 minutes as part of the test. Nonetheless, I do agree it is definitely in the interests of the PLAN to get a 300kg payload rotary UAV that is about 1 deck high and not much wider, otherwise the 056 will be forced to undergo significantly more drastic changes to accomodate it. BTW you can get a dipping sonar for ~50kg, and sonobuoys for 8-10kg each. The SUV200 is already close to the height of one deck. A little wider is possible, for maybe a slightly bigger engine, but who knows if the space between the torpedo launchers is enough to fit a UAV capable of lifting 300kg.
Yeah the SUV200 is only an example showing that they already have the technology to do it, but the real deal can't be based on that airframe, it's simply too small and not compact enough for shipborne operations. Just look at DASH, it's pretty much just a huge engine with rotors on top and a torpedo under its belly. Ideally they should make one with a turboshaft engine.