I do timesheets for client billable work and for internal work. I find the system for the type of work I do to be a bit silly. But we have done some things to hlep make it easier. We have an application that queries on 15 minutes to enter the task you are working on. If it is still the same you can just ok it and keep going. I do have a problem with the hours out of office as occasionally an epiphany will come and I find myself booting up and doing some code in the middle of the night. Which I then have to enter into the system and do the explanations for. But the company I work for weighes results before anything else so I am not really pressured about it.

Now as for making it a metric. For any metric to work, an understanding of the work process must happen. For people coding, talking about cricket is important. The down time where you can subconsciously or peripherally reflecton the task at hand is valuable. Fresh eyes and fresh minds help the process. If this is not understood by the people using the metrics you can find artifical limits or performance guidance set. At the same time, I have found people are different in how they approach tasks and how optimally the work in given constraints. Some people who see down time in the work enviroment will abuse it. How do you see this in recorded metrics of the type you site without first reviewing the quality of work produced. It seems the metrics being asked for would only be secondary to a higher level metric.

Every company is different, every team is different, every person is different and each task is unique.