Drawing on self-determination theory, this study focuses on the person- and occasion- specific components of the daily dynamics of employees' global psychological need satisfaction at work. Predictors (job demands related to information and communication technologies, segmentation norms, and workload) and outcomes (perceived productivity, psychological detachment, work-family conflict, job satisfaction, and personal satisfaction) were also examined across both levels to better grasp the mechanisms underlying these short-term dynamics. A total of 129 French employees filled out questionnaire surveys at the end of each workday for five days (521 observations). Results from Dynamic Structural Equation Modeling (DSEM) showed clear associations between need satisfaction, the predictors, and the outcomes at the person-specific level. However, and although need satisfaction levels were found to fluctuate on a daily basis, they seemed immune to the effects of daily fluctuations in predictors levels, and unlikely to generate matching fluctuations in outcome levels. These results suggest strong homeostatic processes protecting employees' functioning against daily fluctuations, but that the accumulation of such fluctuations over the work week may jeopardize these processes.