Despite researchers considering time of day an important variable in studies on implicit food evaluations and food intake, time of day effects on implicit food evaluations have yet to be tested. Positive implicit evaluations of unhealthy food stimuli measured with an implicit association test (IAT) predict behaviour toward those stimuli, and are assumed to reflect automatic reactions outside of conscious awareness and control. However, recent research has revealed controlled processing to have an influence on IAT performance. The current study tested time of day effects on implicit evaluations of unhealthy food measured with an IAT, and specifically on automatic and controlled processes underlying IAT performance. A sample of 304 undergraduate women aged 17–25 years completed a single-category IAT at varying times of the day. Results revealed that participation later in the day was associated with a more positive implicit evaluation of unhealthy food. This was mediated by a decrease in the ability to inhibit positive food reactions (i.e., controlled processing), rather than an increase in automatic positive reactions. The findings draw attention to the importance of considering time of day in studies measuring aspects of implicit cognition using tasks such as the IAT.