Tintamarre has a beautiful beach, but you are missing out if that's all you see on your visit. The island is much larger than you might think and provides an opportunity for hours of hiking and exploring. The interior of the island contains the remains of an airport and many old homes, all abandoned decades ago. There are also several little ponds and an additional beach to the one that the boats stop at.
If you get far enough from the beach, you are sure to see some of the island's resident goats (I saw at least ten on my visit). Their presence is also apparent when you suddenly emerge from the brush into an area that looks like it's been mowed with a lawnmower - very striking.
I definitely recommend bringing lots of water with you if you explore the island. It is much hotter in the interior than on the beach, and of course there aren't any facilities at all. You should also wear long pants if you really want to explore, as much of the island is overgrown.
It would probably take a good five hours to really see the whole island, but you can see quite a bit even with less time, since a lot of the ruins are fairly close to the beach.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.