Best months to visit Playa Larga are November/December through April. The reef at Playa Larga is close to the shore.
SNORKELING: The best time for snorkeling is in the morning with calm sea. Towards the afternoon the sea becomes rough. WEATHER: The best climate is during the dry season (from November until April). May and June is worth a try. Avoid July until October, it's rainy season and there is a higher chance for hurricanes. TOURIST CROWDS: July and August are the Cuban summer holiday and it might get crowded in general. Usually Playa Larga itself isn't that crowded at all. There are casa particulares only, not even one big hotel.
Birding at National Park Zapata is outstanding. We did this guided tour twice with different guides at different months. A car is necessary to go to this three different places.
The best time of day for birding is the morning. Don't go too early, otherwise mosquito might eat you up.
The best months are November until April in the dry season. Rainy season from July until October is not recommended, as areas can be flooded. Shoulder season May and June, showers may occur but easier to find a casa without booking in advance. July and August are the Cuban school holiday.