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It takes about 5 business days from the date the RFE is MAILED. INS may generate RFE and mail it several days later. So if you know hwen your RFE was mailed, you can expect to receive it 5 days later.
So far as your second questions goes, I do not have any answer. Reply to my RFE was received by INS on 8/1/2001 and I am still waiting.