Perhaps this timer program would work for you
http://www.macworld.com/article/1167..._features.html
I actually bought Timer Utility Pro on the Mac App Store but for some reason it's no longer available. But the web site has a non-Mac App Store version available.
Timer Utility Pro has a time tracking feature that allows me to set billable rate and has a stopwatch feature that lets me pause and resume the countdown. It exports to a CSV text file which can be imported into a spreadsheet for reporting purposes.
I'm fairly sure there are other timer programs that can do the trick for you.