The assumption that mood remains constant when unaffected by task stimuli is an implicit but integral part of neurocognitive research, but it remains largely unexamined. The purpose of this study is to test the hypothesis that periods of rest and simple tasks lower participants’ mood, an effect we call “passage-of-time dysphoria.” This would empirically demonstrate the long-intuited phenomenon that mood is sensitive to the passage of time. This hypothesis and related ones have been confirmed in (1) a set of “online participants” collected at the National Institute of Mental Health and (2) an exploratory sample of 5,000 “mobile app” participants who played a gambling game on their smartphones. This exploratory sample was randomly selected from a dataset collected by our co-authors at University College London (UCL). We are preregistering the same analyses that were performed on the exploratory sample of mobile app participants for a held-out, confirmatory sample of 21,896 of the mobile app participants collected by UCL.