Just some further research, as a former maths/science teacher I am always weary of using "mean" as an indication of time. It seems, after some research, it seems that there are many "outliers" that have affected the data set above. Some of the outliers took 12 years and 8 years! They had their reasons.Hence I found the median, which is a better indication and it was 13 months. So this could move relatively quickly.