Once upon a time in England, a very mean witch was terrorizing the local population, who finally went to see a wizard to see what could be done about her. The wizard gave them a potion that would turn the witch into a statue.
The townspeople managed to put the potion in the witch's food. When she found out about this, she turned green with rage, but it was too late and the potion worked as expected.
The jubilant population had a big celebration and parade, and placed the petrified witch in a park as a public example.
Pretty soon, people discovered that the witch had been frozen in a position that made her a perfect sundial, and started using her to tell the time of day. The custom grew and even today, people often refer to 'Mean Green Witch Time'.