BACKGROUND: Burr hole drainage is the mainstay of treatment for chronic subdural hematoma (cSDH). However, the impact of the interval between diagnosis and surgery on clinical outcome is unknown. This study investigates whether surgical timing affects outcome in patients with mild to moderate symptoms who do not require immediate surgery. METHODS: We performed a single center, retrospective cohort study of 330 surgically treated cSDH patients with a Markwalder Grading Scale score of 1-2, at the Amsterdam UMC, between 2012 and 2022. The interval between diagnosis and surgery was measured in hours and dichotomized (surgery within vs. after 24 h). To account for potential confounding by hematoma mass effect, patients were stratified based on midline shift (greater than 10 mm vs <
10 mm). Primary outcomes included reoperation rate, complication rate, 30-day mortality, length of hospital stay and discharge destination. Univariable and multivariable regression analyses were performed for each stratum. RESULTS: The mean age of the cohort was 73 years, and 241 (73%) were male. The median time to surgery was 25 h (IQR 15-54). Among the 330 patients, 157 (48%) underwent surgery within 24 h after diagnosis. Patients who received early surgery (<
24 h) had a significantly higher proportion of midline shift >
10 mm compared to those undergoing later surgery (56% vs. 34%, p <
0.002). The use of anticoagulant or antiplatelet therapy did not differ between groups (47% vs 54%, p = 0.27). No significant association was found between surgical timing and any primary outcome across all strata. CONCLUSION: In patients with cSDH presenting with mild to moderately symptoms, the timing of surgery did not affect clinical outcome, particularly as delayed surgery did not result in poorer outcomes. These findings suggest that postponing surgery to daytime hours may be safe in this subgroup. Validation in prospective studies, ideally incorporating functional outcomes, is nevertheless required to confirm these results and guide clinical practice.