Using location-based services (LBS) data from the third ring area in Fuzhou city, this study analyzes the spatiotemporal characteristics of block vitality by measuring the density of active population gatherings. It explores the spatiotemporal heterogeneity of block vitality based on a geographically and temporally weighted autoregressive model (GTWAR), considering built environment features such as POI density, functional mix, and road network density. Additionally, it investigates their interactions using a geographic detector and compares differences between weekdays and weekends across five daily periods. Key findings include:(1) The overall urban vitality in the region exhibits a spatial pattern of “one core, two centers, multiple sub-centers, and multiple clusters” and undergoes spatiotemporal dynamic changes across five periods, characterized by ‘dispersion, agglomeration, deep agglomeration, and dispersion.” (2) The marginal effects of POI density, functional mix, and road network density on block vitality exhibit instability in both spatial and temporal dimensions.(3)Interaction effects between two factors exert a more significant impact on block vitality than the effects of individual factors, with interaction types including dual-factor enhancement and nonlinear enhancement.(4)Differences exist in the spatiotemporal characteristics of block vitality, built environment influences, and their interactions between weekdays and weekends.