You can select which labor unit (minutes, hours, or price) opens as default when adding labor to line items within your project. 

To do this, just go to Settings > Company > Defaults, then scroll to the bottom and you will see a section titled "Labor Units." Select the unit you prefer to work with, and click "Update Workflow Options."

The next time you add labor to a line item within the Builder, the labor unit you selected will show up first by default.