Abstract Optimal sensorimotor timing hinges on the generation, refinement, and employment of internal models to meet task demands. In finger tapping sensorimotor synchronization tasks, this occurs across and within tapping conditions that prompt externally-cued synchronization, followed by un-cued continuation. Theory suggests within each condition, initial behavioral performance is adjusted by internal models. However, whether distinct within- and between condition subprocesses are associated with activation of unique neural networks remains unknown. During fMRI, 100 neurotypical adults completed a finger tapping task with synchronization and continuation conditions. Rapid improvement in tapping accuracy occurred during the initial seconds of both synchronization and continuation conditions. Tapping performance in the first few seconds of each condition was marked by heightened functional activity across sensorimotor, prefrontal-parietal-temporal, and salience network regions compared to subsequent within-condition performance, suggesting rapid refinement of an internal model. Intensity of functional activity within the same regions correlated with task performance. Findings highlight dynamic processes supporting development and refinement of internal models for sensorimotor timing.