The Test of Variables of Attention (TOVA) is a continuous performance test (CPT) that assesses attention, impulsivity, and processing speed. CPTs are used in the assessment of attention-deficit/hyperactivity disorder (ADHD) in children, but more young adults are being assessed for ADHD as well. The TOVA norms are based on a standardization sample that was tested early in the day, and any TOVA administered after 1:00 p.m. will be flagged as potentially invalid. Whereas the testing time recommendations make sense for pediatric samples, it is unclear whether they are appropriate for young adults in college, who typically show significant phase delay in their diurnal rhythms. In addition, many college students consume large amounts of caffeine, and it is unclear how caffeine consumption affects TOVA performance. The current study examined the impact of time of day, self-reported diurnal preference, and caffeine consumption on TOVA performance in a double-blind, placebo-controlled experiment with healthy college students. There was evidence of diurnal variation on average response time and impulsivity but not on overall ADHD score, with participants tested in the afternoon responding faster but making more commission errors than did participants tested in the morning. Caffeine consumption led to significantly faster response times, but only for participants who typically consumed relatively little caffeine. We conclude that the TOVA can be administered to young adults outside the recommended time constraints without compromising the validity of test score interpretation but that the caffeine consumption of participants should be closely monitored.