It is well established that the circadian rhythm system plays a crucial role in metabolic regulation. Yet, the influence of time of sample collection in cross-sectional, untargeted metabolomics datasets remains underexplored. We therefore investigated the temporal oscillations of 853 serum metabolites from 5954 fasting samples in the Hispanic Community Health Study / Study of Latinos cohort, where blood samples were drawn within a short daytime window (7:45 am - 1:38 pm). In total, 84 serum metabolites were significantly associated (p