My wife has been in the US for about 2 years of the needed 3 to begin the neutralization process. I am curious about the requirement or 18 months physical presence. Does that mean cumulative 18 months, or do they have to be consecutive? If we take a trip back to visit her family in China for a few weeks, does that start the clock over? Does she need to hit the 3 year mark before filling out the N-400?