The ACS Committee on Trauma specifies prehospital criteria that trigger trauma team activation (TTA). The study aims to define the relationship between TTA and time of day, mechanism of injury, and need for operative intervention. All trauma patients presenting to LAC+USC (January 2008-July 2018) after triggering TTA were screened. Patients were excluded if time of ED arrival was undocumented. Demographics, injury data, and outcomes were analyzed. After exclusions (<1%), 54,826 patients were enrolled. The median age was 35 [IQR 23-53]. The median Injury Severity Score was 4 [1-10]. The most common mechanisms of injury were falls (n = 14,166; 31%), auto versus pedestrian collisions (n = 11,921; 26%), and motor vehicle collisions (n = 11,024; 24%). Penetrating trauma comprised 16 per cent (n = 8,686). The busiest hour for TTAs was 19:00 to 20:00, although penetrating trauma was most common between 23:00 and 01:00. Emergent surgical intervention in absolute numbers was most frequent between 20:00 and 01:00. As a proportion of the number of TTAs per hour, emergent operative intervention was most frequent between 23:00 and 06:00. In conclusion, the volume of TTAs and the triggering mechanism of injury vary significantly by time of day. The need for operative intervention is highest overnight. This information can be used to help increase hospital preparedness and allocate resources accordingly.