Are you discounting the Kobold Hall adventure in the DMG? Put that together with Mike Mearls's comments on how he'd improve the final encounter, and you've got a good showcase for the new rules. When we played it, it easily filled (and perhaps exceeded) a four-hour slot.

There's also the Free RPG day scenario, but that might not be as easy to lay hands on now. Still, perhaps a local friend picked it up and can share it with you.