Background: Spontaneous breathing trials (SBTs) are a core component of ventilator liberation in adult intensive care unit (ICU) patients receiving invasive mechanical ventilation (IMV) and are recommended in standardized weaning protocols. Prior studies suggest ventilator liberation occurs more frequently during the day, possibly due to differences in staffing, workflow, and sedation practices. However, limited evidence exists on whether SBT frequency differs between day and night shifts and whether such differences are associated with patient outcomes. Objective: To compare SBT frequency between day shift (07:00–18:59) and night shift (19:00–06:59) and evaluate associations with extubation frequency, ICU length of stay (ICU LOS), and mortality. Methods: A quantitative, retrospective observational study was conducted using the eICU Collaborative Research Database. Adult ICU patients receiving IMV with documented SBT-related ventilatory activity (pressure support) were included. Shift timing was derived from time-stamped data. Descriptive statistics, chi-square tests, and independent samples t-tests were performed using IBM SPSS Statistics. Results: A total of 1,397 SBT-related events were analyzed. SBTs occurred more frequently during the night shift (65.9%) than the day shift (34.1%) (p < .001). Extubation occurred more frequently during the day shift (58.8%); however, no statistically significant associations were found between shift-based SBT frequency and extubation (p = .127), ICU LOS (p = .796), or mortality (p = .197). Conclusion: Although SBT frequency differed significantly by shift, it was not statistically associated with clinical outcomes. However, observed patterns suggest clinically meaningful differences, with higher SBT frequency at night and greater extubation frequency and slightly higher mortality during the day, likely to reflect differences in staffing, physician availability, and clinical decision-making rather than SBT frequency alone. These findings support readiness-based ventilator weaning practices across shifts and demonstrate the importance of timely progression to ventilator liberation following SBT completion, without unnecessary delay and clinically appropriate.