Complicated appendicitis is associated with high morbidity, mortality, and healthcare costs. However, the relationship of preoperative in-hospital delay >24 hours with complicated appendicitis and postoperative morbidity remains unclear. This meta-analysis investigated the effects of preoperative in-hospital delay on complicated appendicitis and postoperative morbidity in patients with acute appendicitis. This study adheres to the PRISMA 2020 and AMSTAR 2 guidelines. The PubMed, Embase, Cochrane Library, and Web of Science databases up to October 14, 2023 (updated on March 16, 2024) were searched for randomized controlled trials (RCTs) and observational studies that evaluated the effect of preoperative in-hospital delays of >24 hours on acute appendicitis. Odds ratios (OR) and 95% confidence intervals were also determined. We yielded 18,130 records, of which 28 studies (512,881 patients) were included in the meta-analysis. The risk of bias was considered serious, moderate, and low for 24, 3, and 1 study, respectively. Although preoperative in-hospital delays of >24 hours were not associated with a higher risk of surgical site infection (OR 1.04, 95% CI 0.97, 1.12, P=0.25), in-hospital delays of >24 hours was a risk factor for complicated appendicitis (OR 1.60, 95% CI 1.25, 2.05, P=0.0002), and postoperative complications (OR 1.51, 95% CI 1.30, 1.75, P<0.00001). In addition, an in-hospital delay of >24 hours before surgery increased the OR of postoperative mortality (OR 1.81, 95% CI 1.33, 2.45, P=0.0001). The sensitivity analyses also confirmed the robustness of our results. An in-hospital delay of >24 hours is a risk factor for complicated appendicitis, postoperative complications, and mortality. Given the subsequent adverse outcomes of in-hospital delays, appendectomy should not be delayed for >24 hours.