A female hamster is pregnant for a little over a month. You should be able to tell that she is pregnant by her increase in nesting habits and larger girth about 4 or 5 days before birth. In 5 weeks she should give birth.
They are usually pregnant for 16 days give or take a day or two. While she is pregnant limit how much you pick her up and also after she delivers try not to pick her up that much. It should not take more than 3 weeks for her to deliver the baby hamsters.