It took 2 weeks for me
RFE was for medicals.
As per my lawyer, it really depends on if all the other checks on your case have been completed at the time of RFE.
As per him, RFE response envelopes have seperate bar code on them and they are routed directly to the officer on your case bypassing the mail room routing. So it should reach him in less than a week, it really seem to depend on if there are no other things pending.
I feel RFE in general is a ggod thing meaning your case is being actively worked on and that it will get approved soon.
Hope this helps