This study provides new findings on the flexible activity of Prolemur simus in an anthropogenically modified habitat in the rural commune of Tsaratanana, eastern Madagascar. Based on camera-trap data, we compared the temporal distribution of activity of one group of lemurs between the forest edge and the forest core. We also investigated the possible influence of nocturnal luminosity on the activity cycle. The analysis was conducted using Kernel Density estimates and the R package OVERLAP. The distribution across the 24-h cycle confirmed that Prolemur simus is cathemeral in the wild. The lemurs displayed three peaks of activity: one during the night and two coinciding with morning and evening twilights. The highest proportions of nocturnal activity occurred at the forest edge and at low moon luminosity suggesting a possible anti-predator and/or human-avoidance strategy. The flexible activity of Prolemur simus may contribute to the tolerance of this Critically Endangered species to anthropogenic disturbance.