Actually, regarding the time frame, 9 years is about half-way through the nodal cycle, as the positions of the north and south nodes reverse at that time, so the full cycle is really 18 years to complete.
susan

Today in the monthly Transit discussion I asked that very question. The answer that was given was that it is the overall effect of the star field as it is hitting earth. The south node is where it was and the north node was the direction it was travelling to.

Supposedly, the effect of what was started in the time of a particular lunar node cycle can take up to 9.? years to complete.