Twelve Hour Island

So here's a story idea that could be realistic or surreal: Imagine an island which has come up just to the surface of the ocean.  During high tide, it's under water - during low tide, it's a wide stretch of damp sand.  And people live on this island.  They've anchored their homes into this sand on stilts, and they live on fish and salvage, and their kids swing across ropes from one house to the next.