The last time I visited Yoko (like 1-2 weeks ago) I had a similar experience in that we started 15 minutes late. I had arrived 10 minutes before my scheduled time, so I had to wait almost 25 minutes. I did the main course at the end though, and the session ended up lasting an hour, despite the delayed start, so I was ok with it.
That could be one way of getting your money's worth, because given her high service standards, Yoko will not ask you to leave before you finish. But I do agree that her popularity seems to be causing start time delays.