Well it honestly depends not necessarily on the amount of hubs, but the quality of each hub and the work you do to the hub. What I mean by work is social bookmarking to get the work indexed and such and such.
It might take months for a hub to mature and become indexed. Hub Promoting is very important.
Try sites like reddit, stumbleupon, and digg to start off and see the difference in page views and earnings!
Anyway, to anwser the question: The first month I wrote about 20 hubs and then proceeded to enter the social bookmarking world. I am at month seven now, and am about to receive my first check from both adsense and hub ad program, which is 100 and 50 dollars respectively.
What is so awesome is that once you have built a solid foundation od quality hubs, the revenue generates itself (called residual income).
Hope this helped!