They got shorter in practice. Especially post-lockdowns lots of people are phoning it in to well paid jobs whilst working from home with Netflix on, taking long lunches, playing with the kids and then doing unchallenging work like meetings with other people who are also phoning it in. Yes they "work" 40 hours a week in theory but this sort of work would have seemed completely alien to someone in Keynes' era.
Another thing to note is the length of retirement has increased significantly since Keynes' time. So if you look at a person's whole life, the amount of time at work certainly has decreased.
