DRJAD, as you may have read, I was recently in the same boat - got the test done on the 7th attempt having not flown for 5 weeks.
While I can't comment on how long it takes for YOUR skills to 'go rusty', only mine, what I would say is that I was pleasantly surprised by how well I flew. In the early part of my training I found that a lay-off of more than a week would allow my skills to deteriorate, but towards the end I was quite happy after several weeks.
If your school/club currency rules allow it (mine didn't) - just do a few circuits before the test and relax! If you go into it thinking you'll fail, you may well do so.
The three examiners at my club are also instructors there and they were well aware from talking to their colleagues how well I could fly. I get the imperssion that with so few good weather days in winter, they were happy to make allowances for my rustiness rather than waste time doing a couple of extra hours tuition before the test. When I did make mistakes, the examiner was quite happy to let me simply try the manouver again.
Get the test done the first chance you get - you may not get another chance for ages! If you fail, it will probably be a partial pass, and at least you've got 2 or 3 hours more experience and will definatley pass the next time.