Background The association of sleep onset time and duration with cardiometabolic health is not well characterized. Methods and Results This study included 6696 adults aged 20 to 80 years from the NHANES (National Health and Nutrition Examination Study) 2015 to 2018. Participants were categorized into 9 groups according to the cross‐tabulation of sleep onset time (<22:00 [early], 22:00–23:59 [optimal], and ≥24:00 [late]) and duration (<7 hours [insufficient], 7–8 hours [sufficient], and ≥9 hours [excessive]), with optimal sleep onset time and sufficient duration as the reference. The primary outcomes included hypertension, hypertriglyceridemia, low high‐density lipoprotein cholesterol, hyperglycemia, central obesity, and metabolic syndrome. Inappropriate sleep onset time and sleep duration were associated with increased odds of hypertension, hypertriglyceridemia, and metabolic syndrome, especially among participants aged 40 to 59 years. Compared with men reporting optimal onset and sufficient duration, men reporting optimal onset with excessive duration (odds ratio [OR]: 2.01 [95% CI, 1.12–3.58]) and late onset with insufficient duration (OR, 1.74 [95% CI, 1.13–2.68]) had higher odds of metabolic syndrome. Compared with women reporting optimal onset and sufficient duration, women reporting optimal onset and insufficient duration (OR, 1.61 [95% CI, 1.11–2.32]) and early onset and excessive duration (OR, 2.16 [95% CI, 1.30–3.57]) had higher odds of hypertension, and women reporting late onset and excessive duration (OR, 5.64 [95% CI, 1.28–6.77]) were at the highest odds of hypertriglyceridemia. Conclusions Late sleep onset as well as insufficient or excessive sleep duration are associated with adverse cardiometabolic outcomes, particularly in participants aged 40 to 59 years. 6 Circadian rhythm misalignment due to loss of sleep, social jet lag, early morning start, and delayed bedtime is becoming common in our modern society, and it is difficult to disentangle the independent effects of sleep duration and sleep onset time on cardiometabolic health outcomes. Consequently, the present study aimed to investigate the independent and joint associations of sleep onset time and sleep duration with cardiometabolic health outcomes, using data from the US NHANES (National Health and Nutrition Examination Study) 2015 to 2018. Furthermore, to evaluate the joint effects of sleep onset time and sleep duration on the odds of cardiometabolic health outcomes, we created dummy variables of 9 categories according to the cross‐tabulation of sleep onset time (early, optimal, and late) and sleep duration (insufficient, sufficient, and excessive). As optimal sleep onset time combined with sufficient sleep duration was treated as the reference, we explored the joint associations between sleep parameters and 6 components of cardiometabolic health outcomes. The associations of sleep onset time or sleep duration with cardiometabolic health outcomes were presented in Table 2 . Compared with the optimal sleep onset time, early and late sleepers had a higher prevalence of hypertension (OR, 1.17 [95% CI, 1.01–1.35]) and hypertriglyceridemia (OR, 1.28, [95% CI, 1.01–1.60]), respectively. The OR of hypertriglyceridemia in individuals with excessive sleep duration compared with individuals with sufficient sleep duration was 1.34 (95% CI, 1.06–1.70). 20 Consistently, our study found that insufficient sleep duration (<7 hours) was detrimental to cardiovascular health. Similar to previous studies, we observed that excessive sleep duration (≥9 hours) was also related to higher odds of cardiometabolic health outcomes. 13 , 21 Thus, the present study provides additional evidence that sleep duration of 7 to 8 hours promotes healthy outcomes for adults. The evidence on the relationship between sleep onset time and cardiometabolic health outcomes is scarce, with only a few studies having investigated this relationship. 34 , 35 Understanding the complexities of how sex‐specific body composition contributes to the risk of cardiometabolic health outcomes can provide important insights into the mechanisms that underlie these diseases. The biological mechanisms underlying the association of multiple sleep characteristics with cardiovascular health are intricate and multifaceted. These results from a large, nationwide, randomized sample survey can be generalized to the adult noninstitutionalized population in the United States. Second, to minimize the effect of reverse causality, we focused on participants without cardiovascular disease, cancer, or pregnancy at enrollment. More important, we separately examined the independent and joint association of sleep duration and sleep onset timing with the prevalence of cardiometabolic health outcomes, thus improving the comprehensiveness and accuracy of the analysis. However, several limitations of this study warrant attention. First, sleep health is an important contributor to general health and well‐being, encompassing dimensions such as sleep duration, timing, efficiency, daytime alertness, sleep quality, and insomnia, forming a multidimensional construct. However, we have used statistical procedures to control for multiple comparisons and our results were found significant or marginally significant using a stringent cutoff of 0.05 after adjustment for multiple tests, thus limiting the chance of false positive results. Conclusions In conclusion, our study provides evidence that late sleep onset time, as well as insufficient or excessive sleep duration, were associated with an increased odds of cardiometabolic health outcomes, particularly in participants aged 40 to 59 years. Moreover, late onset combined with excessive duration had the highest prevalence of outcomes. Our findings encourage the adoption of healthy sleep habits to prevent the development of cardiometabolic health outcomes. Sources of Funding None. Disclosures None. Supporting information Tables S1–S7 Figures S1–S8