This contribution leans on ergonomic research developed during a thesis on temporal management in dynamic work situations. We present a temporal categorization based on different social science approaches. This categorization is operationalized through the analysis of middle-manager activity in horticultural production. We first specify the temporal requirements in terms of intertwined timeframes which these workers manage within a complex “temporal work environment”. We then set out our methodology, based on interviews in nine French nurseries and horticultural sites and on systematic observation of five “chefs de culture” (middle managers in charge of horticultural production) during their activity. We analyze the different ways in which these workers consider the timeframes and deal with their temporal environment. The results have led us to suggest four complementary temporal concepts to understand multimodal temporal behaviour in dynamic situations. Our model thus distinguishes between: a “pushed by the past” time (1), a “pulled by the future” time (2), a "built by the present” time (3), and an uchronic time of “past alternatives” (4). These temporal conceptions are mobilized to analyze temporal configurations relating to work requirements, which lead to difficulties and risks that the “chefs de culture” treat, as part of their activity, as risks both for production and for workers’ health.