I will answer you based on my experience as a human resources manager. I've also worked on many cases on the ground.
Based on the discussions we've had with municipal representatives, I think the ideal time frame for a regulatory project is three years. Beyond that, the process is too lengthy. Four years is a very long time. After seven years, everyone has had time to change roles and, ultimately, you have to start all over again.
So I think three years or less is reasonable. Beyond that period, it seems to me that we are straying from the reality of municipalities or organizations.