Final answer:
During a Plan-Do-Check-Act improvement project, changes are implemented during the Do phase.
Step-by-step explanation:
In a Plan-Do-Check-Act improvement project, the implementation of changes occurs during the Do phase. The Plan phase involves identifying the problem and developing a solution, the Do phase involves carrying out the planned changes, the Check phase involves evaluating the outcomes of the changes, and the Act phase involves implementing the changes on a wider scale if they are successful.