Your wedding is the same day as mine!!!! ... but yours is earlier!!
Our wedding will start at 4 PM at the chapel then at 5:00 PM the ceremony in the GCR gazebo and then a beach front cocktail + private reception from 6 to10 PM.
We did our site visit last june.... I think Albatros is very nice, I love the beach view and the air-con is sooo necessary during June!!!! So, if you decide to go for the 3 PM I recommend Albatros or Marias, though I'm not sure you can do the 3 pm at Marias, since it's only open for dinner. From that 2 options, the more private is Marias, since it's only available trough reservations, but you don't get the same view as Albatros.
The Sunset Grill is nice too, we had dinner once there and I liked the view of the Laguna, you may ask what time is the best to catch up the sunset and that will be nice too. Gaviotas is very near to the biggest pool so, at least during the weekend that I spend there (the 2nd of june '11) was usually noisy during the day, but during dinner it seems nice and quiet.
I hope that can help you!!!
Good luck with your planning!!