I am bumping this post b/c I have the same question and same problem. I hope yours is solved by now. If not, I can tell you (from experiance this week), that it isnt cleared out yet on the 3rd day after you have taken it. (I definately have an infection (fever, chills, back pain at my kidneys, smelly and cloudy urine, increase in freq/urg, etc.), but I had some Macrobid at home and took it, trying to take care of it before it got bad, since it was a weekend. Unfortunately, it didnt work and by the time I went to the Dr, nothing showed up b/c the Macrobid was masking it.
One thing that might help you is going to a drugstore and buying a home UTI test kit. (They are usually over by the pregnancy tests.) They dont pick up on all types of UTIs, but they can pick up on some of them. It is best to get the first urine specimen of the day, as that is the strongest, least diluted.
That is what I am doing right now. The only downside is the tests get kind of expensive. (There are 3 to a box, and the box cost $18.) But, they may be cheaper where you shop.
If anyone out there has any idea how long it takes, pls let us know. That would be a HUGE help!