Does AdSense work on Subdomains?  The answer is 'yes' they do. AdSense approval is supposed to take a week, but some have experienced over a month or wait time. AdSense users are required to comply with the Google Webmaster Guidelines so it's a good idea to meet these guidelines before you apply. There are some theories and fact on how to avoid approval delays and rejections when applying for AdSense. "How many subdomains are acceptable to use with adsense? There is no stated limit.

AdSense approval facts

1. A site with a bad or overly minimal site navigation may get rejected or delayed. I recommend at least 5 links leading to pages with unique text content.
2. A site without content or content that's unique may get rejected or delayed. Your posts should be at least 250 words or more.
3. A pay-to site is grounds for rejection. These are sites that that pay people to perform activities that drive more traffic to the site or sites that encourage users to click on ads.

AdSense approval theories

1. Creating a blog at hubpages.com allows you to create an AdSense account and guarantees you acceptance. The same would apply for creating a Blogger blog.
2. If you create 10 posts with unique content on your blog, before you submit it to get approved for Google AdSense, you're guaranteed approval.

Here's an official blog posts from the AdSense blog 'Before you apply to AdSense'. The date on the blog post is 2008, but it's the most recent post they've made on the issue.

Here's an official support page from Google: Help to get your application approved

Here's a helpful link: AdSense Program Policies