I'm a good swimmer but not snorkeler. I have a low gag reflex so sometimes just putting a snorkel in my mouth is a trying experience. We've done the snorkeling at CC 3-4 times now and have some great pictures of all of the items they've put into the water including Mickey and Minnie. The first time we did it, I did it for DH who really wanted to do it. I was able to use the snorkel once my head was in the water and able to control the gagging but only if my head was in the water. I went out to see Mickey and Minnie and figured we'd been out for about 15-20 minutes which was about as good as I figured it was going to get. When we got back to shore, I checked the time and we'd been out for over an hour! I was stunned - it didn't seem that long at all. So I guess it was easier than I thought.
One thing to remember though - given that it turned out that we were out for a long time, I recommend VERY HIGHLY that you wear a t-shirt so that your back doesn't get burned. I'd been warned about this by a friend and was very glad that I'd done so.