JohnCow has a post up with information on how long it can take to make money from your blog.
Here is a snippet from his post:
A lot of new bloggers seem to think that once you’ve setup your blogspot.com account and you’ve written your first article, you’re set. Slap a couple of ads on and you can start planning your early retirement. If only..
The only thing that will make your blog money is you. Setting up the blog and providing it with (good or interesting) content is only half the the work. You’re going to have to sell yourself the best way you can –with your words.
I think the whole thing is interesting to read, but a little light on the key information that the post sets out to answer. He sums it up saying that it depends on the blog, and honestly, that is very true. It depends on the blogger, the blog, the subject, and how well linked and like the site is, but when it comes down to it, I would say that for the best bloggers, you are looking at around six months or more. Some bloggers won’t see a dime until their blog reaches the one year mark or more. It really depends on how aggressively you market your site.
If you are not bringing in some revenue by the six month mark and making money from your blog was your goal, then it is time to reassess what is going on with your site.
If you need help figuring out why your site isn’t monetizing well, feel free to purchase some time from me with my consulting service, and I will help turn your site around.