Whether you always charge by the hour for your services of use this infrequently, defining your charging rates is a useful way to save time by being able to select from a preset selection.
Select the 'Settings' icon in the left hand menu bar and select 'Billing'.
From here, you can see that you have a default rate which can have a description and cost per hour.
By selecting the + sign to the right of this rate will allow you to add a further rate. For example, Standard Rate, Out of Hours, Discounted etc.
Setting Chargeable Time Increments
Your business may charge by the hour or part hour; in which case, you can set up the increments by which your field workers time is charged.
In the same screen, (Select the 'Settings' icon in the left hand menu bar and select 'Billing'), under the Payment Terms you can adjust the time increments in which you wish to bill (in minutes):
Don't forget to select 'Save' before you move away from the page.