I am a freelancer, but, I typically only do gigs that are a pay for output, not for time.
My husband does both, but, I think he just uses the sample invoice I game him to track and invoice his time.
The only thing I don't like about him using this system is that he has no running total of how much he has billed (I do the taxes and want to get an idea of what to set aside for April).
I'd be interested in hearing what others use.