Under Settings > Work and projects > Durations, you can select what durations are displayed in the options list when adding an event or a task. With events, the duration is calculated based on the starting time of the event.
Tick the durations you'd like to use in your Scoro site. You can use either single menu or separate menus for hours and minutes.
Since this setting is available under the Work and project section of the Settings, this affects the whole site, which means that all users will be using the same task and event durations.