Some writers think it's a jinx to send a query; it will only get you an automatic rejection. I don't believe that, but I do know that editors don't want to feel "pushed." My rule of thumb is to add 30 days to the editor's own estimated response time. That's one reason why I use the "official" RTs on my web site instead of a possibly more realistic one, which you can find on my "Response Times" page or at http://critters.critique.org/blackholes.
One comment on sending your manuscripts via certified mail: DON'T. It's considered amateur. Since our mss are only copies, and sent unsolicited, most editors resent having to sign for them. Some will refuse them. Always send your submissions by First Class mail. If you're really nervous, you can include a SAS-Post Card, which most editors will return. However, for short stories many editors consider any form of acknowledgement of receipt attempt as the mark of a beginner. Remember, even if you've never had a story published, you want to come across as a professional. You can read more about this at Mary Soon Lee's fantastic writer's resource web site (http://www-2.cs.cmu.edu/~mslee/wr.html), or most books on the business of writing (try your library).
By the way, some editors allow simultaneous subs. If they do, it will be stated in their guidelines. Just don't send a sim-sub to any publication unless they say it's okay.