Purpose <p>The aim of this study was to examine the associations between chrononutrition variables (time of first meal, time of last meal, and eating window) and thyroid function.</p> Methods <p>A cross-sectional study was conducted among 608 healthy adults aged ≥ 18 years. Chrononutrition variables were collected through a face-to-face interview. Fasting blood samples were collected to measure serum thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) levels. Multiple linear regression analyses were used to evaluate associations between chrononutrition variables and thyroid hormones.</p> Results <p>Among 608 healthy adults, later timing of the first meal was associated with higher TSH levels. In the fully adjusted model, participants who had their first meal after 08:30 had higher TSH levels than those who had their first meal at or before 07:30 (β = 0.56, 95% CI: 0.07 to 1.06; P trend = 0.02). In contrast, the time of last meal after 19:00 was not significantly associated with TSH levels (β = -0.07, 95% CI: -0.66 to 0.53; P trend = 0.63). An eating window longer than 11&#xa0;h was also not significantly associated with TSH levels (β = -0.45, 95% CI: -0.97 to 0.08; P trend = 0.09). No significant associations were observed between the chrononutrition variables and FT3 or FT4 levels.</p> Conclusion <p>Our study suggested that the time of first meal, rather than the time of last meal or eating window, may be particularly relevant for TSH regulation.</p>