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Delays in surgery for patients with acute appendicitis may increase the risk of perforation and complications. These risks must be balanced with the theoretical risk of nighttime operations.To determine the effect of (i) time of day of surgery and (ii) time between triage presentation and surgery, on surgical complications in patient undergoing appendectomy for appendicitis.Population level data from Ontario from 2009 to 2015 was used to conduct this retrospective cohort study. The primary exposure was (i) time of day of surgery and (ii) time between triage and surgery. The primary outcome was a composite outcome of perioperative complications. Conditional logistic regression adjusted for patient factors was used to estimate adjusted odds ratios (OR) between the exposure and complications.Twelve thousand nine hundred thirty-seven matched pairs (N = 25,874) of adult patients were included. Compared to day operations, the odds of complications were lower during the evening (OR, 0.90; 95% confidence interval [CI], 0.84–0.96) and no different at night (OR, 0.90; 95% CI, 0.77–1.04). The odds of complications were higher in patients who waited longer than 24 hours for surgery compared with those who waited less than 6 hours (OR, 1.27; 95% CI, 1.14–1.43) with no increased risk in those who waited 6 hours to 12 hours or 12 hours to 24 hours.This large population study is the first to assess surgical risks using a case-crossover design to account for the surgeon as a potential confounder. Nighttime surgery and delaying surgery up to 24 hours were not associated increased risks of complications.Therapeutic, level III.