For a study, researchers sought to determine how long postponing therapy for stage III-IV non-small-cell lung cancer affected patient survival. Cox regression analysis with penalized smoothing splines was used to examine the relationship between treatment delay and all-cause mortality for stage III-IV lung adenocarcinoma and squamous cell carcinoma using data from the National Lung Screening Trial (NLST) and the National Cancer Database (NCDB). The NCDB compared cumulative survival in patients who received “early” versus “delayed” treatment using propensity score-matched analyses (i.e., 0-30 versus 90-120 days following diagnosis). According to Cox regression analysis of the NLST (n=392) and NCDB (n=275,198), the hazard ratio decreased the longer therapy was delayed. There were no significant differences in survival between patients with stage IIIA, IIIB (T3-4, N2, M0), IIIC, and IV (M1B-C) adenocarcinoma and patients with stage IIIA, IIIB, IIIC, and IV squamous cell carcinoma in a propensity score-matched study (all log-rank P>0.05). Delay in therapy was related to increased survival in patients with stage IIIB (T1-2, N3, M0) and stage IV (M1A) adenocarcinoma (log-rank P=0.03, P=0.02). The results remained consistent in a sensitivity analysis that considered wait time bias. In this nationwide study, patients with stage III-IV adenocarcinoma and squamous cell carcinoma who received treatment 3-4 months later had no lower overall survival than those who received treatment immediately. These data could help inform decision-making in the continuing COVID-19 epidemic.