Going down on a girl: how long you do you want me there?

Don't leave the area permanently until she has an orgasm. Leaving for a moment to tease other areas is fine and good but make sure you return for the big "O". Sometimes I want another one and sometimes I don't so just ask her if she would like more:)
P.S.
The more comfortable you make your woman the faster she will come

I say until she cums once. Then after that your just teasing.

I would say no longer than 5 minutes. After that I would get impatient and frustrated.

Stay down there for as long as it takes you to get the job done and that means giving her a fantastic orgasm and she's totally finished and satisfied. You only come up when she signals you that she's had enough which will probably be shortly after she's finished cumming. My boyfriend and I aren't into any other stuff yet, only that, and I'd say he's pretty. . as you say. Impeccable at doing that so it satisfies us both and he feels lucky to get that. Sometimes he does get a quick hj afterwards Other than that, we're more into going out like to movies and doing things together or having fun with friends. This girl isn't getting pregnant by some stupid accident. lol.

Im thinking that if your technique is so impeccable than you really already know by now. You would know that the girls will let you know that they have had enough. Or you would know from the evidence that you have done your job. To me it sounds like you not very sure about this experience. And in my experience, if a guy still has questions about it. His technique is not impeccable and still needs some work. impeccable = in the know

Until she cums. Or picks your big head up. She'll probably signal you in some way.

I say ask your partner. Every person is different about what they like and how long. The biggest thing is to let her know that it is okay for her to tell you what she wants without you taking it personally.

Many women are afraid to tell a guy anything because they are afraid it will hurt the guys ego. If she can feel comfortable with telling you what she likes and doesn't then she will be able to tell you how long she enjoys you being there. She might also tell you what works and doesn't work for her making you even better at your job.