We knew an executive director of a nonprofit who did a time study (tracking her time by 10 minute intervals) that showed that she was spending more than 40% of her time on the business of the board—supporting them, preparing for meetings, engaging in board communications, attending meetings of board committees, and so on.
While we would hope that staffing an advisory council would not require that same time commitment or intensity of work, don't underestimate the work involved. Our experience tells us that the best advisory councils are well-staffed. By "well-staffed" we mean that they have a staff person working with them who cares about the people involved, who makes the work of the advisory council a priority, and whose annual performance is measured in part by the quality of support he/she provides to the advisory council. Keep in mind that "quality of support" is often directly related to the amount of time a person has available to provide that support.