This paper posits the postcolonial history of Senegalese toxicology as an ongoing effort to sustain the temporalities of advancing careers, collective development, technical innovation, cumulative knowledge and public protection. In the face of ending transnational collaborations, waning means, equipment breakdown or new patterns of intoxication, Senegalese toxicologists struggle to remember, recount and reactivate the lost rhythms and futures of their scientific activity. In this paper, I consider various implications of writing intense preoccupations with the promises and fragility of continuous, progressive time into the history of science. First, I suggest that the orientation and fragmentation of time opens new possibilities for the analysis of science as politics in its engagements with the political economy of toxic hazards in Senegal. Secondly, I discuss the different ways in which progression and its interruptions qualify this history as postcolonial. Finally, I explore how scientists’ historical accounts and temporal desires might relate to Michel Serres’ reflections on non-linear models of the time of the history of sciences.