Nuffnang ads are hard to understand(or am i just a stupid boy) :(

 Last Month, I started blogging. I started with a movie blog for everyone. Luckily, it was able to get enough traffic and last week, I started joining paid ads. I joined nuffnang and adbrite. I wonder why nuffnang ads are available only in a particular time, and the rest, its just sleeping. The nuffnang team said that it is just based on campaign ads. I don't know campaign but I believe that ads should be available for the whole day because the traffic is just being wasted