Can prawns and lobsters live out of water for more than six hours?
TL;DR version is they are gill breathers and need to be in a humid and moist environment to have a considerable longer life span outside sea water.

Dr. Cowan's on being asked the same question about lobster said: 


  “Gills work best in seawater, but if lobsters are kept in containers of seawater with no aeration, they quickly use up the oxygen and suffocate,” she said. “That it why it is imperative to transport lobsters in containers with no standing water.” - New York Times


Many lobsters, shrimps and even crayfish &amp; crabs are transported in boxes with a small amount of water in the bottom and they survive for several days like that. However the long term side effects of this are still to be discovered as most crustaceans transported this way get cooked.