Previous studies indicate differences in short-term postoperative outcomes depending on the surgical starting time of the day, but long-term data are lacking. The aim of this study was to clarify if surgical starting time of the day influences long-term survival in gastric cancer patients. This cohort study consecutively included 2728 patients who underwent curatively intended gastrectomy for gastric cancer in 2011–2015 at a high-volume hospital in China, with follow-up until June 2019. Cox regression provided hazard ratios (HRs) with 95% confidence intervals (CIs) for 3-year all-cause mortality, adjusted for age, sex, health insurance, pathological tumor stage, surgical approach, neoadjuvant therapy, and weekday of surgery. Compared with patients with early starting time of gastrectomy (08:00–09:29), the point estimates for 3-year all-cause mortality were modestly increased in patients with a starting time in the middle of day (09:30–13:29; HR 1.15, 95% CI 0.97 to 1.37) and later (13:30–21:25; HR 1.10, 0.91 to 1.32). The corresponding HRs were increased particularly in patients who underwent laparoscopic gastrectomy (HR 1.54, 1.10 to 2.14 and HR 1.59, 1.12 to 2.25, respectively) and in those with stage II tumors (HR 1.74, 1.11 to 2.73 and HR 1.60, 1.00 to 2.58, respectively). Our study indicated that in patients who underwent laparoscopic gastrectomy and in those who with stage II tumors, starting surgery in the early morning might be associated with better long-term survival.