It will interrupt your work. Do it anyway and do it for the entire day. Pick a happy medium in defining what constitutes a new activity. This last column is totally subjective. Some people experience tremendous stress as they face how they actually spend their time.
Some people are delighted to see how much they actually accomplish.
The data on the Time Log is useful. Analyze the activities to see how much time is spent in a reactive mode, what accounts for interruptions, and what times of day you are most effective. File it away and repeat the exercise in a few months to follow your progress. This is a delusion. The goal isn't to try to figure out how to do every good thing, but to develop our ability to choose what's important from among them.