Timed and Flat Rate Services on Quotes and Invoices

I see that when constructing a new quote, and using the "add a manual line item" we can select Flat Rate Services. But, we cannot select Times Services. It would be helpful if we could select from our list of Timed Services as well. If we've gone to the time and trouble to set up both timed services and flat rate services, it stands to reason we should be able to further benefit from that streamlined and time-saving feature by being able to select either timed or flat rate services to apply into both quotes and invoices.