The brain’s ability to bind incoming multisensory stimuli depends critically on their temporal structure. Specifically, there exists a window of time wherein multisensory stimuli are bound together, affecting perception and performance. Although recent evidence suggests that multisensory temporal processing is malleable in adults, no study has looked at whether this temporal window of integration can be narrowed. We used an audiovisual simultaneity task to determine the malleability of the temporal window’s boundaries, subjecting 24 participants to a perceptual learning paradigm wherein feedback was given as to the correctness of their audiovisual simultaneity judgments. Results show that the temporal window was narrowed by 29% (from 291 to 177ms), the effect was stable for one week after training, and a similar effect was seen in subjects’ susceptibility to the Flash-Beep illusion. Furthermore, the effects were specific to active training: subjects passively exposed to the identical stimulus set without feedback showed no performance improvements. This generalization indicates alteration of a common multisensory pathway and has strong implications for future manipulation of performance on more complex tasks. Given recent evidence for an expanded temporal window in neurodevelopmental disabilities such as dyslexia and autism, these efforts may lead to more effective diagnostic and remediation tools.