The 24-hour format is a style setting of the Events module. In Focus Plus, click the module, open the Styles tab and go to Date. Switch Display time on, then switch Display time in 24-hour format on and leave Display AM/PM off. The setting applies to that module instance. If Date format is set to Custom, the time switches are not used; write the time into the custom pattern with HH:mm for 24-hour or hh:mm for 12-hour.
The Events module of the free Focus theme shows the date only; displaying the time is available in Focus Plus.