Hi Nicolene,
Out of the box, there isn't a way to do this. It's based on the unit that is used at the leaf level work item.
There may be a way to do this with Customizations. Here are 3 resources that we offer to help you handle customizations:
Reach out to your dedicated CSM if you have one
Post to our Customizations Q&A Forum where our customization experts respond and monitor regularly - https://success.clarizen.com/forums/22175706-Customizations
Attend our Advanced Q&A session currently available a couple times per week - http://www.clarizen.com/resources/online-demo.html#second