Our perception of time varies considerably from moment to moment, but how this variability relates to endogenous fluctuations in attentional states has been neglected. Here, we tested the hypothesis that perceptual decoupling during spontaneous mind wandering episodes distorts interval timing. In two studies with different visual subsecond interval timing paradigms, participants judged their attentional state on a trial-by-trial basis. Mind wandering states were characterized by underestimation of temporal intervals and a decline in temporal discrimination. Further analyses suggested that temporal contraction during mind wandering, but not the decline in temporal discrimination, could be attributed in part to attentional lapses. By contrast, we did not find any robust evidence that metacognition pertaining to interval timing was altered during mind wandering states. These results highlight the role of transient fluctuations in attentional states in intraindividual variability in time perception and have implications for the perceptual consequences, behavioral markers, and costs and benefits, of mind wandering.