The purpose of this study was to investigate sleep patterns in competitive youth swimmers and to establish any time-of-day effect on physiological and psychological variables linked to swimming performance. Twelve swimmers (14.8 ± 2.1 years) underwent physiological and psychological tests in morning and evening and completed sleep diaries over a 2-week period. There was a non-significant effect between morning and evening swimming performance for 800 m (p = 0.068) and 50 m (p = 0.306). Handgrip strength was significantly greater in evening (p = 0.007), back and leg strength were significantly greater in morning (p = 0.013). There was no time-of-day effect for jump height (p = 0.756). The profile of mood states indicated significantly higher anger (p = 0.012) and vigour (p = 0.000) in the morning. Swimming performance was not significantly affected by time of day; however, physiological variables showed varied results. Multiple factors could be influencing results including training time and mood state so should be monitored closely by coaches.