Early mobilization has been proven to be an effective and safe intervention for preventing complications in mechanically ventilated patients; however, there is currently no unified definition of the optimal mobilization initiation time, hindering widespread clinical implementation. As clinicians are increasingly aware of the benefits of early mobilization, the definition of early mobilization is important. The purpose of this study was to evaluate the effects of different early mobilization initiation times on mechanically ventilated patients and rank these times for practical consideration. The Chinese Biomedical Literature Database, the Chinese Knowledge Infrastructure, Wanfang Data, PubMed, Cochrane Library, Web of Science, and Embase databases, along with grey literature and reference lists, were searched for randomized control trials (RCTs) that evaluated the effects of early mobilization for improving patient outcomes; databases were searched from inception to October 2018. Two authors extracted data independently, using a predesigned Excel form, and assessed the quality of included RCTs according to the Cochrane Handbook (v5.1.0). Data were analyzed using Stata (v13.0) and Review Manager (v5.3.0). A total of 15 RCTs involving 1726 patients and seven mobilization initiation times (which were all compared to usual care) were included in our analysis. Network meta-analysis showed that mechanical ventilation for 48-72 h may be optimal to improve intensive care unit acquired weakness (ICU-AW) and reduce the duration of mechanical ventilation; however, there were no significant differences in length of ICU stay according to mobilization initiation time. The results of this study indicate that initiation of mobilization within 48-72 h of mechanical ventilation may be optimal for improving clinical outcomes for mechanically ventilated patients.