We just got back and if you really want to feed the dolphins, I would do it first thing!!
These boards are great!!!
We went to SW 3 times during our recent trip, we just got back last night. Two times we went directly to Dolphin Cove at opening. The boys, DS7 & DS9, and I would go right to the dolphin area and my husband would go to the fish hut and wait in line to purchase the food. The fish hut (where they sell the fish to feed - $5 for a tray) is not well marked and most people (non-DIS'ers) it seemed - didn't seem to know you could buy fish. Right before they open the Fish Hut the SW employees would get on the microphone and tell the people the best way to interact - how to hold your hands, remove your hats, etc.. and purchase food. If you wait until they make the announcement, the line will be huge.
When we went, they were opening the fish hut at 9:30am, but I've read sometimes its at 9:15am. Anyways, both times we were able to feed the dolphins.
Also, they-the dolphons- must know when it's time to eat because our second time waiting, we got to pet a bunch of dolphins way before we were feeding them. They were looking for food.
The experience only makes us want to do Discovery Cove more! Maybe next time!