It depends on what the code is. If I'm working on writing unit tests for relatively simple code taht didn't have any tests when it was origionally written I can

It depends on what the code is. If I'm working on writing unit tests for relatively simple code taht didn't have any tests when it was origionally written I can do 30 hours a week with out to much trouble. If I'm doing new development for non-trivial features I generally can't get 30 hours in unless I get lucky and get in the flow several days during the week.