This article explores the subjective and temporal modes of organizing underlying science-based social movements through an analysis of two mother-led movements in Argentina. The Abuelas de Plaza de Mayo appropriated forensic anthropology and nascent DNA technologies to identify their disappeared grandchildren during the 1976–83 dictatorship. The Madres de Ituzaingó Anexo developed community-led epidemiology studies and agrochemical contamination mapping to argue for a causal relation between intensive pesticide use and high rates of childhood illnesses. We focus on how these movements delineate visions of time, responsibility, and collective action by closely examining the underlying histories and practices of each social movement as they politicized motherhood and appropriated scientific practice. We offer the concept of mother-led science through the temporal registers of constancy, desgaste, and durability to illuminate the iterative relationship between care work, creating sustainable communities and institutions, and the fragile processes of stabilizing facts. Mother-led science, with its dual claims to scientific authority in an epistemic register and maternal authority in an affective register, articulates a potent form of scientific organizing. We suggest that these affective temporalities may be present across all science-based social movements but can be obscured by narratives of linear progress toward objective truths.