Abstract Background Inadvertent delays in access to appropriate therapeutic interventions in high-risk group coronavirus disease 2019 (COVID-19) patients contribute to mortality in patients with severe/critical disease presentation. Objectives The aim of this study was to determine the effect of timely admission to the hospital on mortality of patients with severe/critical COVID-19. Another secondary aspect of this study was to observe the efficacy of time-dependent use of corticosteroids on mortality of critical/severe COVID-19 patients. Methods Clinical data of 659 patients with severe/critical COVID-19, admitted to four major tertiary care hospitals from the Islamabad-Rawalpindi region of Pakistan was retrospectively collected from a period February–August 2020. Multivariate logistic regression analysis was carried out to determine the predictors of mortality in severe/critical COVID-19 patients. Results Out of a total of 659 patients, 469 (71.2%) patients died. Age > 60 years, presence of hypertension, heart disease and kidney disease along with late admission (>5 days) were significant predictors of mortality in patients with severe/critical COVID-19. Conclusions The study highlights the importance of well-timed provision of appropriate medical interventions control COVID-19-associated mortality.