Las Piñas has a tropical climate, and the most important factor in timing a visit is the monsoon. The dry season runs from December through April, with December to February being the most pleasant months — warm but not oppressive, and low chance of rain. March and April are hot (35°C+) and humid before the rains break.
The wet season (June to November) brings heavy rain and the risk of typhoons, which can disrupt travel across the Metro Manila area. September and October are statistically the worst months for typhoon activity.
The single best reason to time a visit to Las Piñas specifically is the Bamboo Organ International Music Festival, held each February. A week of concerts by international organists, both in Saint Joseph's Church and in other venues, it is the event for which Las Piñas is known internationally. Advance planning is needed as accommodation in the Metro Manila area fills during festival week.