Background and purpose Rapid therapeutic decisions in acute stroke patients leading to earlier initiation of revascularization therapies are associated with better outcome. An association between regular working hours and reduced time to initiation of intravenous thrombolysis has been reported. However, its influence on mechanical thrombectomy (MT) remains uncertain. We aimed to analyze the effects of admission time on door-to-groin time and stroke outcome in a large prospective stroke registry of the Neurovascular Net Ruhr in Germany. Methods Procedural times of a total of 512 patients treated with MT were analyzed. Admission to hospital during regular working days and hours (Monday to Friday, 8 am to 4 pm) was compared with admission outside these times. Door-to-groin time and the difference in NIH Stroke Scale between admission and discharge served as primary outcome parameters. Long-term functional outcome was centrally assessed with modified Rankin scale. Results MT outside regular working hours was associated with a significant mean initiation delay of 20 min. By multivariate regression analysis, every 20 min delay of MT reduced the difference in NIHSS score between admission and discharge by 0.76 points (95% CI −1.24 to −0.28, p = 0.002). Favorable long-term outcome did not differ between both treatment groups. Conclusions Treatment outside regular working hours caused a significant delay in the initiation of MT, which was associated with a decreased short-term clinical efficacy of thrombectomy. Strategies like compulsory attendance of the interventional neuroradiologist at the hospital 24/7 might result in shorter door-to-groin times and consecutive in better stroke outcome.