Recent studies have revealed that temporal perception can be changed in sensor-motor cycles. The mechanism for this may be Bayesian inference; our beliefs regarding the cause--effect relationship can influence our temporal perception as we can anticipate the outcome. The Bayesian paradigm has also been incorporated into studies of collective behaviours by agents interacting through time. However, the cause--effect relationship in the real group inevitably intertwines and may invalidate Bayesian inference relying on a solid cause--effect relationship. This study investigated temporal perception of synchronised group clapping. We found that the intensity of temporal binding on the perception of group clapping increases with group size, supporting the Weber--Fechner law of temporal perception. In addition, we apply the temporal Weber--Fechner law to a simple theoretical model. As a result, this law explains how the frequency increase of group clapping is influenced by the group size, known as joint rushing. These findings suggest that the change in temporal perception following the law generates complex group dynamics.