This article is from the FAQ, by with numerous contributions by others.
Thanks for maintaining the USA Immigration FAQ:
I have a few unanswered questions. I am planning to
submit a petition based on immigrant classification as
an alien of extraordinary ability. What are the major steps
(milestones) towards obtaining the GC after you submitted
the petition? What is the typical duration of each step if
the petition is based on extraordinary abilities?
Step 1: Filing the petition with INS
(Adjudication times vary from 4 weeks to 10 months depending upon
several factors, such as extent of documentation, place of
Step 2: Filing for adjustment of status (I-485) or consular processing
ADJUDICATION TIME VARIES FROM 8 WEEKS TO 14 MONTHS DEPENEDING
UPON YOUR PLACE OF RESIDENCE)