It only took me a month, or 1.5 months, before I only needed to shave maybe once a week, or less.
I mean, your mileage may vary (obviously), but hormones usually do a lot for various areas of body hair (and less for others). Three months in, for me, and my arm hair is so thin, you can hardly see it, even after over a week of not shaving. I think my results are probably more dramatic than average, however.