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Accurate control of stimuli timing is essential in psychophysical experiments, yet the stimulus onset asynchrony (SOA) specified within a virtual reality (VR) application may differ from that physically delivered to the participant. This study presents a wearable wireless sensor framework for measuring physical audiovisual SOAs on a trial-by-trial basis during VR experiments. Visual onset is detected using a photodiode-based synchronization marker, whereas auditory onset is detected directly from the analog audio signal using a portable wireless sensing module. The framework is characterized across different rendering pipelines, audio buffer configurations, spatial audio conditions, and wired and wireless headset connections, and subsequently validated during psychophysical experiments under both stationary and walking conditions. Before compensation, systematic audiovisual offsets ranged from 118 to 185 ms across configurations. Condition-specific temporal compensation reduced mean SOA errors to approximately zero, although residual trial-to-trial variability remained, with standard deviations of 11–32 ms. During psychophysical validation, the framework successfully measured physical audiovisual onset in 99.94\% of trials. These results demonstrate that trial-by-trial physical monitoring can complement conventional pre-experimental calibration, enabling behavioral responses to be associated with the audiovisual timing actually delivered on each trial and supporting more accurate and reproducible audiovisual psychophysics in dynamic VR.