I’ve had some results same day.  Trichomoniasis seems to take the longest.

Is usually 24 hours

You can ask the agency what tests they use. (Normally, I'd look up some refs for you but I don't have time. Well, here's one: http://www.differencebetween.net/science/difference-between-antibody-test-and-pcr-test/ ) E.g., for any given disease there may be a "fast" test, like maybe a dip stick test based on an antibody, that is less sensitive and less selective than a PCR test that can take overnight or 24 hrs.. If you're being charged, the PCR test might cost more than the antibody test.
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You can google stuff like "How do they test for __[enter STD here]___?" and see if they give the turnaround times for each KIND of test.

See if you have a "Any Test Now " locations near you.  24 to 36 hours turn around. Also the email the results directly to you .

viral tests  .. i.e.   HIV , HSV 1 & 2  etc can be next day ..  bacterial  i.e..  syphilis, Trichomoniasis  etc can take 2 to 3 days  

i use  stdcheck  --  you dont have to provide an ID , so can keep it discreet with a "hobby name"

Go to stdcheck.com , you could even use a gift card to stay anonymous. Then you can pick a quest diagnostics lab in safeway, near you. If you go in the morning most likely, you will have your results the same day. And while you're getting your s t d screen , you can also do a regular blood draw to check your cholesterol and all that good stuff too. Typically, for a whole panel, it's about two hundred and fifty dollars