Timing theorists asume that prospective timing is
functionally equivalent to many other perceptual and cognitive
tasks in that it is a deliberate, controlled process that requires
attentional resources... In this view, concurrent temporal and
nontemporal tasks compete for limited resources, with the result
that less attention is devoted to timekeeping than otherwise would
be the case. The fewer resources devoted to time, the more
inaccurate and variable the time judgements.