How can we create time balance definition based on custom time attribute

Summary:

We have a requirement to sum up the time card reported hours if entered on Capitalized project / Task (the capitalized flag is enabled on Projects module). So we created a custom time attribute and enabled on time layout, to retrieve if a Project - Task combination is Capitalizable or not. The custom attribute value is read only and populated based on user-inputted project & task entry.  

To calculate the total no.of hours reported on the capitalized project - task, we wanted to create a time balance definition using this custom time attribute. But there is no option to create a time category (enabling the tracking) with the custom time attributes.