Did it about 5 times in September and said something to staff about I can't imagine in winter as the snorkel coves are cold water. They said it's actually much more comfortable then because you aren't going from hot hot air to cold water. I thought, yeah right ...
Took whole family for Christmas and it was our best trip yet. I was able to constantly go in and out of the snorkel areas because it didn't take me forever to ease in. The "resort" pool area and "lazy" river water was so soothing as it was so warm. The wet suits were not hot like warmer months so we weren't pulling them on and off.
I would never hesitate to go in the winter months .... especially since the prices are usually better.