Most beach photographers plan their day around the sunset. In Playa del Carmen that habit works against you. The coast faces east, so the sun comes up out of the Caribbean, with Cozumel a low grey line across the channel, and goes down behind the jungle. For photographs, few months on this coast beat January. It is the dry season, with air far less heavy than in summer, and the sargassum that can pile up on these beaches later in the year is usually at its lowest.
So start at dawn on the town beach. At Parque Fundadores, beside the ferry pier, the Portal Maya, two tall figures leaning together to form an arch, stands at the edge of the sand, and against a sunrise it makes a clean silhouette if you are there before the square fills. Punta Esmeralda, a free beach north of the centre, is quieter, with a freshwater cenote spilling across the sand into the sea. It is popular with local families, so a weekday gives you emptier sand. Let the camera sit outside for ten minutes before the first shot. A lens carried from an air-conditioned room into a humid Caribbean morning fogs over at once.
The high midday sun, the enemy of most beach photography, is when the cenotes work. Their shafts of light need direct sun through an opening in the rock, and each cenote has its own best hour. At Dos Ojos, the large cavern system south of Playa towards Tulum, the afternoon is often recommended, when light slants through the openings and lays beams through the water. The January sun never climbs as high as the summer one, so pick a clear day and be patient.
The Tulum ruins sit on a cliff above the sea, and El Castillo on its edge is the shot everyone is after. The site normally opens after sunrise, so be at the gate for opening. The first hour gives you low sidelight across the stone and your best chance of the Castillo with nobody in front of it. INAH, which manages the site, bans drones and requires a permit for tripods, so travel light.
Nortes, the winter cold fronts that push down across the Yucatán every so often, bring a day or two of wind and choppy water under grey cloud. On those days the Cozumel ferry and the reef boats may be cancelled while inland trips carry on, so spend them inland, on a cenote swim rather than a cenote shoot, since the beams need sun. Move the boat days to the calm that follows, and fit a polariser to cut the glare off the surface. Cozumel's reefs, Palancar among them, are usually calmest and clearest in the morning, before the wind gets up, and on the first still morning after a norte the horizon is sharp and the channel has settled back to turquoise.