I think I started at about 35 weeks, with just one cup a day.
I didn't really take it seriously with number1, just a cup here and there, then ran out of it... My labour was induced at 40+9, I had an ok labour, she was born after 40 minutes of pushing.
2nd time round I did stick with it, I had a quick labour, (3.5cm at 11.30pm, Matthew born at 1.25am, at 40+2) and he was born in 2 pushes.
I know 2nd labours are generally quicker though.