To change the time for a detention type, navigate to the 3 lines menu, click on "School Settings" and then click on the "detentions" option under the "Detentions" tab.
Find the detention type you would like to edit, and click on the pencil icon next to it.
You will be presented with the edit menu for that detention type. Clicking on the "default time" field will display a time selector, which you will be able to scroll to find your desired time.
Clicking the OK once you have finished will save the changes made to the detention type.