This article is from the FAQ, by with numerous contributions by others.
Generally, once the petition is filed, it takes about 30 days to
hear from the INS their approval or denial, then at least another
30 days for the paperwork to be transmitted to the foreign embassy
and for the interview appointment to be arranged. It can take up
to 5 or 6 months total, though usually it is 90 days or so.
 
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