Apply GC for Parents

[vvn]

Got my US Citizenship recently. Planning to apply GC for my parents. Is there a wait time OR can I apply immediately? Current Visitor's Visa of parents expiring during second week of March 2012. Can I bring them here before that and apply GC for them while they are here? Also, Is it true that while they are in the US and I apply GC for them, they can stay back as long as until they get their GC. As stated above, their visitor visa is expiring early March 2012, will they be allowed to travel to the US now. In other words, Is there a cut-off of minimum 60 days or 90 days prior to their visa expiration, that they can travel to the US. Lastly, how long would it take for them to get GC.

[JoeF]

There is no wait time, but it is a bad idea to file for them shortly after they enter on a visitor visa.