Request for Time Tracker Feature: Distinguishing billable vs non-billable hours

Could we please implement a feature in the time tracker that allows us to distinguish between billable and non-billable hours? I would like to be able to track my pre-work, such as preparing project proposals, bids, and initial invoices, without billing the client for that time. However, I do want to track these hours overall to ensure that I am pricing my design services correctly.

Having this distinction would also help when I send clients status reports, as I could filter out the non-billable hours. Thank you for considering this request.