Motivation influences how time flies when you’re having fun.

Numerous studies have shown that a positive state, relative to a negative state, makes time appear to pass more quickly and causes assessments of elapsed time to be shorter. Gable and Pool examine how the degree of motivation - as distinguished from positive or negative valence (as in approach versus withdrawal) - influences subjective time:

Time flies when you’re having fun, but what is it about pleasant experiences that makes time seem to go by faster? In the experiments reported here, we tested the proposal that approach motivation causes perceptual shortening of time during pleasant experiences. A first experiment showed that, relative to a neutral state or a positive state with low approach motivation, a positive state with high approach motivation shortened perceptions of time. Also, individual differences in approach motivation predicted shorter perceptions of time. In a second experiment we manipulated approach motivation independently of the affective state and showed that increasing approach motivation caused time to be perceived as passing more quickly. Finally we showed that positive approach motivation, as opposed to arousal, shortens perception of time by comparing a highly arousing positive state with a highly arousing negative state. Shortening of time perception in appetitive states may prolong approach-motivated behavior and increase the likelihood of acquiring appetitive objects or goals.