Avoid cruise ship days. It's completely crowded. If you can't avoid go early not later than 9 a.m. or in the afternoon. Sea is calmer in the morning. Of course best with sunlight. April and May higher chance for sea turtles.
The dry season last from December until April/May. Cruise ship season last until late March. Rainy season from June until November with the possibilities of hurricanes and flash floods. The driest month is March and the wettest is August.
It is a popular and great reef for snorkeling and diving. You can rent the equipment for snorkeling and diving at the entrance. They have nice and experienced guides. They request a small fee of 2 $. The restaurant offers fresh prepared food, lunch and fresh fruit juices were delicious. We were there twice, once at a cruise ship day and once without. At our first visit it became crowded after 10 a.m. and the second visit was really great and only few people. We spent there many hours with several times snorkeling. The bubbles at Champagne Reef are nice. We saw a huge variety of fish and corals.
To get to the best place for snorkeling walk until the end of the rocky beach. A rubber mat helps you to get into the sea.