Had to keep track of work I did for one of my 3 divisions in order to get the division heads to see I was being overburdened. It worked beautifully. The division that expected the most out of me has switched an annual project I do for them over to an off-site secretary. I was practically doing cartwheels down the hall after I heard of that decision!
It took a lot of time, however, to document all that work. I found myself taking shorthand notes of the main work I did, and relying on my memory for the frequent interruptions. At the end of the week I'd transcribe the notes onto an Excel log sheet and add in an estimated time for various interruptions. Even with all that written down, I still think I worked more for that division than showed up on paper.
I've got to keep up the documentation in order to get the off-site director to realize that the 6 guys he's got me reporting to at our facility take up a big percentage of my work day. In other words, taking away the one project was a wonderful start, but it's not all that needs to be done.
As far as setting up the Excel sheet to keep track, you could make columns of your most frequent duties and write in the various time periods spent on those duties in rows going across. At the end of a week or month, you could then total up the columns to see what kind of a percentage of work is done on each duty.
Also, keep extra columns handy for those duties that come up out of the blue.
Movinonup 
