You can take Nankai Airport Express down to Izumisano. From there, you can get a map from the tourism board which is just beside the train station, it takes 20mins to walk to the fish market if no stopping. You can check on Hyperdia Website on the train timing. The fish market is quite small, 30mins to an hour will be enough to visit the fish market. It depends on whether you want to see the Auction sale. It starts at 14:30 every day except Wed. and Sun. Hence, you can adjust your time based on that. I only have time for morning so i missed the auction sale.There are also mini flee market outside the fish market on the day i visited. If you want to try the fresh sashimi don, you can have it inside the fish market, there is one small shop which had the very nice and fresh sashimi don. There is a stall at the corner which sell all the fried seafood stuff, good to try out.