Ten minutes total.
It used to be much more casual. You didn't used to have to pay per person, meaning that two people could share one tray of fish and each share in the feeding experience. You used to be able to feed as soon as you paid and got your fish. Now, you have to pay per person to enter the feeding area, and once everyone enters they pass out trays of fish to each person and everyone feeds when instructed. If only part of your family wants to feed the dolphins, then only those who pay can enter. Other family members must stay out of the area, and the non-feeding viewing area is not very good for viewing other family members who want to watch the rest of their party feeding the dolphins. I liked it when everyone could share in as many or as few trays of fish as they wanted to purchase.
Also, the feeding experience is very regimented...almost like a military operation. The group must listen to a set of specific instructions, fish are passed out to the attendees, you hold onto the fish until further notice, then you are allowed to feed in a "ready, set, go" sort of way (they don't actually say ready, set, go, but that's my characterization of it). The entire experience was over in just a few minutes. Of course, then a photo of your dolphin feeding experience is available for purchase.
It's ok for those who want to try it out and don't mind the expense for the rare opportunity to interact with a dolphin, but compared to the old way of doing things, it's just not as fun and casual. As it is now, I preferred observing the dolphins at my own pace from the side of the pool, underwater, and from the overlook.
For fun, unique, and casual feeding experiences I highly recommend feeding the sea lions and rays. Both are lots of fun. Feeding the sharks is also available, but they are not always hungry. However, when the sharks are hungry, it's fun to watch them get excited.