No Schedule, it happens all day. As you enter the park, head to the left to the Key West area. You pass the sting ray tank, then walk down to the dolphin lagoon area. Good to go early. At 10am, trainers come out with a bucket and feed certain dolphins and make them do tricks.
Yes, there is a line up for the fish food. The window opens for about half an hour, then closes when all the food is sold. I think it's $4 for 4 fish. Annual Pass Holders get a $1 discount. No age limit. Yes, it's worth it. You'll get to touch the dolphin, and pet them. At DC, you have more time, get a kiss, and a ride to shore. At the Key West area, the dolphins only come up to those with the food. If you get lucky, they'll hang out and let everyone pet them before swimming away. If they come up for the food, and you don't give it to them, they splash you. Once all food is sold, the window closes, and there is about an hour wait for the next feeding time. The dolphins won't come up to anyone during this time, although the trainers will tell people to gently leave their hand in the water still, just to make it seem like they might come up.
For the sting rays, you can touch their wings as they swim by. Feed them early because once they are full, they don't eat anymore.
The Sea Lions are fun to feed. They stand in front of the people and bark like dogs.
Bring lots of cash. I'd say about $30. The fish go fast. Most people by 3 cups at once.