The diving season in Bohol is year-round. Expect some monsoon rains between July and September. But it is generally too far south to be affected by the rainy season typhoons. Chartered dive boats running from Mactan Island on Cebu down Balicasag often include a stopover at Cabilao Island on their itineraries. This site is often patrolled by schools of hammerheads.
Sightings are common shortly after sunrise or just before sunset.
The best dive is on the edge of a sand-flat which projects westward from the point at the northwest tip of the island. In addition to the sharks, you may see large barracudas and game fish. Colonies of garden eels live in the sand-flat. When they poke their heads out of their holes to feed, their upper bodies sway in the current like a living carpet of long grass. As you approach they'll withdraw quickly into the sand.