Depo Provera typically takes around 3 months to wear off after each shot. This time period can be, and often is, increased when depo provera is administered regularly. Many forums focused on women who have used depo provera report that users often have trouble getting pregnant for weeks or months after the shot has worn off.
The length of time Depo Provera stays in the system varies. Most women can get pregnant from four to ten months after use but it typically takes about two years before fertility is restored to normal. Here's the link for more information: http://www.babyhopes.com/articles/depopregnancytest.html.