Try to be as descriptive as possible and focus on those duties or tasks that you performed on a regular basis.  Do not attempt to recall every unique task you performed, particularly if you only performed it once or twice.  Focus on the large picture.

Percentage of Total Time Devoted to Duty

Here again, it is not necessary to "split hairs" on those tasks you performed rarely.  On the other hand, you must be fair and honest in the percentages you state and they must include actual working time.  Do not include time waiting for assignments or training sessions, etc.  But DO INCLUDE both chargeable and non-chargeable hours actually worked.

Description of Duty

This is the most important component of this section.  Attempt to describe the duty as briefly (and yet completely) as possible.  Describe the nature of the task.  Some tasks are more clerical in nature and would not typically require a salaried professional to perform them.  Other tasks require a professional with independent judgment and creative input.  Consider these distinctions when listing your duties and descriptions, but do not classify them as such.  Your description alone should convey what type of task you performed.