Planning time can vary considerably depending upon the scope of an assessment-driven change effort, the size of the organization or community and the extent of participation in the planning process.  Most change projects aim for an 18-24 month reassessment cycle in order to keep people in the organization focused on the effort and accountable for making changes related to it.  I favor a 24 month assessment cycle because it assures that the reassessment is always conducted at the same time of year, eliminating one form of possible variation affecting the results.  In addition, experience has shown that spring assessments that ask people about behavior that was observed or experienced over the past year are more reliable than those administered in the fall after summer vacations.

This 24 month approach is based on the assumption that some evidence of change should be evident in 24 months, providing feedback to the organization that the change effort is working.  It also provides an opportunity for mid-course adjustments.  In my experience with large organizations, hopeful trends are usually seen at 24 months, but the strongest evidence of change effort success often occurs at the 48 or 72 month reassessments.  After that point further improvement is still likely but will occur in increasingly smaller increments.  Smaller, more nimble organizations with focused change projects can often use an annual reassessment cycle to map out progress over time.