The subjective and contextually variable experience of time is a readily accepted concept. However, few studies have examined how individual differences influence established contextual manipulations of the cognitive mechanisms (attention and arousal) central to the dominant theory of time perception, the scalar expectancy theory (SET: Gibbon, Church & Meck, 1984). Impulsive and non-impulsive subgroups are used as a source of interpersonal difference, and context is varied in two ways: presence of click trains to create an arousing environment and through the modality duration is experienced through and division of attention between them. Both contexts influence subjective timing judgements (assessed through pair comparisons), but differential influence of context is primarily observed through interpersonal attentional differences (greater rightward shift in psychophysical function due to an attentionally demanding context in impulsive individuals: F (1, 35) = 4.51, p = .04, η2 = .11). The present study supports the need for a refined cognitive timing model which allows interaction between arousal and attention (Glicksohn, 1996).