I did it. Even went out there a little after sunrise, as advertised. Visibility was horrible, apparently if you had brought some hardcore snorkeling gear you could dive in right by the rocks and then you could finally see something.
I actually didn't make it there until 2 hours after sunrise. If you want to snorkel...
a) Don't expect too much
b) Go earlier than I did
c) Take the tour out to that island
To get there you have to leave town and head towards Playa de las Artistas and pass the waterfall area. It took 20-25 min. from the center of town.