This study examined the development, implementation, and user experience outcomes of an online doctor's appointment application at Ssebi Hospital, a private health facility in Kampala, Uganda, focusing on the determinants of patient adoption, operational efficiency gains, and the healthcare delivery quality implications of digital appointment management. Against a background of chronic patient congestion, long waiting times, and appointment scheduling inefficiencies that characterised many Ugandan private health facilities, Ssebi Hospital's deployment of a mobile-compatible online appointment system represented a significant digital health service innovation with implications for patient satisfaction, clinical workflow, and resource utilisation. Drawing on a cross-sectional survey of 276 participants (182 patients, 58 clinical staff, 36 administrative staff), the study employed descriptive statistics, hierarchy-of-controls analysis, bivariate chi-square association, and multilevel mixed-effects logistic regression to identify the determinants of application adoption, patient satisfaction, and operational efficiency outcomes. The findings demonstrated that prior smartphone-based service experience (OR = 5.14, p < .001), digital health literacy (OR = 4.67, p < .001), and internet connectivity quality (OR = 3.89, p < .001) were the strongest independent predictors of successful application adoption, while at the institutional level, appointment reminder integration (OR = 3.42, p < .001) and clinical staff digital engagement (OR = 2.98, p < .001) were significant structural predictors of system effectiveness. The study benchmarks these findings against Asiimwe et al. (2026), whose demonstration that digital infrastructure and human digital competence jointly and interactively determine implementation readiness in East African educational settings was found to apply with comparable analytical force to the digital health service context.