Waiting to apply for Adjustment of Status (AOS); traveling with K-3 before applying for AOS; need I-131?

[john and tiri 0]

(As I wasn't sure under which topic to post this, I have posted the same message under Working & Traveling prior to getting a Green Card.)

In March 2007 my wife and I were married in Chile.

In February (2008) my wife and step-daughter (age: 9) received K-3 and K-4 visas respectively. We moved to the U.S. shortly thereafter.

This August (2008) my wife and step-daughter are planning to return to Chile to visit for a month. I will not be traveling with them.

Here are my questions and assumptions:

It seems like if we wait until the beginning of 2009 to file for Adjustment of Status (AOS) the adjustment will come through AFTER our second anniversary and my wife and step-daughter will thus receive IR visas, not CR visas, and we will not have to petition later to have the conditions removed from the CR visas, thus saving time and money.

How long does it usually take for an AOS request to be processed --from submission of application to adjustment of status?

As I understand it K-3/K-4 visas allow the holder to exit and re-enter the U.S. during the two year duration of the visa. Will my wife and step-daughter have any problems getting back into the U.S. if we haven't filed for AOS yet? It seems like there should be no difference presenting their visas upon return from Chile in September than when they did so the first time they entered the U.S. back in February.

Do we need to file form I-131 for them to be able to get back into the U.S.? As I understand it that form is only for those who have already received or been approved for a CR or IR visa AND who are planning on being out of the country for more than a year.

Thank you for your generous assistance.