Elle,
I can only speak from my own experience. I think the time varies depending on your specific situation, and just varies from person to person. I started Spring Forest about 6 years ago. I was suffered from insomnia for 1 1/2 years and had tried everything.
Approx. 3 weeks into my practice I just suddenly didn't have it anymore. So for me changes happen in a very "quantum" way.

Message..Faith, Patience, Persistence.

Good Luck!