I've had very good results with Easy Time Tracking - they have a limited free version, which I used for a while to get used to it (I had been using Timeslips, and expensive package used by law firms, but it got very dated), then purchased the full version for 49 dollars. I'm very pleased with it - it has a timer which sits on your screen as a pop up, and it lets you track the various phases of production (which you can customize), and will let you bill as well - although I don't use that feature:
It tracks application usage and open document usage. If you are intelligent about how you name your documents (for example, I include the project code in all my file names), you can use this to track working time per project.
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