I can't remember exactly, think within a week and I had a few hubs? As previously said it's more about the content than the number of hubs. My best advise would be to write about what you know first, this way you can create quality hubs, then if you want to test the waters on other categories, write a hub or two for different categories until you find what is best for you. Some people remove hubs that do not bring in much traffic, however I don't see the point in removing a hub even if it only brings in 100 views a month that's still 100 views.
Currently I have 14 hubs and get around 50-75 views a day across them, but I also have not really done any promoting other than sharing them on facebook/twitter after publishing. I just recently came back on here, I don't think I really been on since around May. I'm not looking into different ways to promote my hubs. :)