码本背景减法与移动的物体

I am trying to use CodeBook method for OpenCV to subtract the background. So far so good, but I am not sure if I can update the codebook for moving objects after some time span, say 5 minutes, I need to update the codebook after which I get lots of moving objects. How do I make sure that after 5 minutes I have a background that needs to be updated? I am trying to use CodeBook method for OpenCV t