Definition
The same value stream is not finished after one round of improvement, but requires multiple rounds of repeated improvement; the source material's experience is about five rounds, each lasting six to eighteen months, which works out to roughly 2.5 to 7.5 years — and the source's own example completed all five rounds within the first two and a half years. These are empirical magnitudes, not a textbook standard.
In detail
The first round of Kaizen eliminates the most obvious waste, and the next layer of problems it exposes must be solved in the next round; doing only one round and moving to the next value stream leaves improvement at a shallow level and prone to gradual relapse. The Five Whys rule reminds us to plan introduction by year, with each round redrawing the current-state map and resetting targets. Five rounds and six to eighteen months are empirical magnitudes, not rule thresholds, and should be written into the plan as customer calibration parameters.
Example in practice
In the first year, a production line reduced delivery lead time from twenty days to eight through Kaizen weeks, and the team originally planned to move on to other production lines. The promotion lead arranged a second round: after redrawing the current-state map, it was found that waiting had mainly shifted to incoming inspection, so the second round focused on supplier quality and Kanban, reducing delivery lead time further to three days in the second year.