The best time to visit Siquijor is during the dry season, from November to May. The peak months are December to February, when conditions are coolest and the seas are calmest for diving. March to May brings hotter temperatures but still dry weather. The island is small enough that even during peak Philippine holidays (Christmas, Holy Week, summer) it feels uncrowded compared to Boracay or Bohol.
The rainy season runs from June to October, with the heaviest rains in August and September. The island can still be visited in this period — days are not necessarily rainy all day — but diving visibility is reduced, and some outdoor sites become less accessible.
Holy Week (April, dates vary) is worth timing a visit around if you are interested in the folk healing tradition: the annual mananambal gathering at Lazi draws healers from across the Visayas. It is not a tourist spectacle, but it is open, and witnessing it is a genuine encounter with the island's character.