OBJECTIVE: Data evaluating timeliness of antibiotic therapy in Clostridioides difficile infections (CDI) are not well established. The studys purpose was to evaluate the impact of time-to-CDI treatment on disease progression. METHODS: A case-control study was performed among hospitalized patients with CDI from 1/2018 to 2/2022. Inclusion criteria were age ≥65 years, first occurrence, non-severe CDI at symptom onset, and CDI treatment for ≥72 hours. Cases included patients who progressed to severe or fulminant CDI; controls were patients without CDI progression. Time to CDI treatment was evaluated in three ways: a classification and regression tree (CART)-defined threshold, time as a continuous variable, and time as a categorical variable. RESULTS: 272 patients were included; 136 with CDI progression, 136 patients without. The median (IQR) age was 74 (69-81) years, 167 (61%) were women, and 108 (40%) were immunosuppressed. CDI progression patients more commonly were toxin positive (66 [49%] vs 52 [38%], P = .087) with hospital-acquired disease (57 [42%] vs 29 [21%], P < 0.001). A CART-derived breakpoint for optimal time-to-CDI treatment of 64 hours established early (184, 68%) and delayed treatment (88, 32%). When accounting for confounding variables, delayed CDI treatment was associated with disease progression (adjOR, 4.6; 95%CI, 2.6-8.2); this was observed regardless of how time-to-CDI-active therapy was evaluated (continuous adjOR, 1.02; categorical adjOR, 2.11). CONCLUSION: Delayed CDI treatment was associated with disease progression and could represent an important antimicrobial stewardship measure with future evaluation.