Abstract <p>Parent–offspring conflict (POC) is a cornerstone of evolutionary theory, yet empirical tests have concentrated on cercopithecine primates, limiting our understanding of how ecological constraints shape conflict expression. We characterized POC behavioral dynamics in mantled howler monkeys (<i>Alouatta palliata</i>), testing whether predictions derived from energy-maximizing species generalize to time-minimizing taxa. We observed 16 mother-infant dyads across four groups in Los Tuxtlas, Mexico, recording maternal rejection, offspring solicitation, and spatial relationships across lactation stages and maternal activities. Maternal rejection increased significantly between early and middle lactation during foraging and inactivity, but was highest during inactivity in late lactation, contrasting with predictions that foraging should be the primary conflict context. Offspring solicitation behaviors (pursuing and following) increased between early and middle lactation but plateaued rather than escalating further. Responsibility for proximity maintenance rested primarily with infants throughout development, reflecting the permissive maternal style characteristic of this species. Time in contact decreased while distance increased across lactation stages regardless of maternal activity. These findings extend POC research to an understudied platyrrhine species and demonstrate that conflict concentrates during whichever activity carries highest opportunity costs for mothers—inactivity rather than foraging in this time-minimizing species—refining the timing hypothesis for application across diverse foraging strategies. Our results underscore the necessity of incorporating species-specific ecology into behavioral predictions derived from evolutionary theory.</p> Significance statement <p>Evolutionary theory predicts that parents and offspring will disagree over how much care parents should provide, a conflict rooted in differences in genetic interests. However, most tests of this theory come from a narrow range of species with similar lifestyles, leaving unclear whether predictions apply broadly. By studying howler monkeys, primates whose time-minimizing foraging strategy results in activity budgets dominated by rest rather than active foraging, we show that mother-offspring conflict peaks during rest periods, not during feeding as observed in more active, energy-maximizing species. This finding suggests that conflict concentrates whenever maternal activities are most critical to the mother's own well-being, whether that involves acquiring food or processing it. Our results demonstrate that applying evolutionary theory across ecologically diverse species uncovers both universal principles and the need to account for each species' unique way of life.</p>