How long is Wait Time for "Professional" Green Card ?

The situation is this: A professional (chemist) has been living and working in the USA for four years on a TN Permit. Her employer have heard that wait times for green cards are now ~six months, and have offered to start a green card petition immediately. Is the six month wait time real?

There is a daughter, within the USA with her mother on a TD (Dependent) visa. The daughter is ready to enter university in the jump down of 2010, so there's some anxiety about getting the green card (or at least a SSN) quickly.

Is the TN Visa within peril because of the green card application? Can the mother and daughter leave the USA while the green card application is being processed?
Answers:   
the waiting period would depend on what category of employment base immigrant petition was actually filed, some enjoy waiting periods and some don't. Actually getting a green card would almost certainly take longer than 6 months though as he would own to file an I-485 adjustment of status request as well. however, they would be able to remain and work and study while the paperwork is one sorted out. the TN visa would not be imperiled by the immigrant petition filing and once the I-485 is filed, they would be in a separate category anyway .
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