I wonder whether the productivity gains would continue if this experiment would last a year or more. I have a feeling that employee motivation went up because

I wonder whether the productivity gains would continue if this experiment would last a year or more. I have a feeling that employee motivation went up because of the fact that something changed - working 32 hours instead of 40, and only 4 days - rather than the actual new reality which they were placed in. We tend to enjoy changes all around, especially if they are for our own benefit. And I do think a shorter work week is a step in the right direction. But how long would it take for those employees to get used to the new reality of a 4 day work week, and going back to old habits of working more slowly during those days? Ideally an experiment would be made with young adults who just started their first job and will land straight into a day work week, and comparing those to the same age group but with a 5 day work week.