When itemizing tasks, don’t forget to allocate time for these tasks:

• Calendar Events
  Make sure to check your calendar for any events scheduled for today, especially if you are not a calendar-driven person. While you can wait until the scheduling phase to add them, it can be helpful to include them in the entire process to increase the awareness of everything you need to do for the day.
• Transitions
  Add extra time or even a separate task for transitions between tasks. Allocating time for set up and clean up for tasks helps you more accurately gauge the total time required for a task. This is especially important for tasks or events which require travel time.
• Daily Activities
  Don’t forget daily activities like eating, exercising or grooming. While these may seem obvious, they take up time in your day, and should be itemized, estimated and scheduled like any other task.

Finally, make sure you account for small interruptions and diversions. The idea is not to measure the effort for each task, but the time you expect to allocate, including interruptions and diversions.

However, if these interruptions and diversions start to take up a large chunk of your allocated time, you’ll need to develop other systems to keep these in check.