This is a standard Oracle Application Express (APEX) calendar region component showing a weekly view on events with a time component. This page allows to choose the time format (12h, 24h) which is being used to display the time component of an event timestamp.

Note the Time Format attribute of the calendar component. It can be set to Default which chooses the time format based on the current locale (e.g. 12h for the US, 24h for Germany). 12 hour or 24 hour force the chosen format independenly from the current locale.