In the last 6 months there have been two major updates where backlinks / indexed pages have updated.
Generally speaking, if you're waiting on a new site to be listed it can take 3 to 6 months for it to be indexed (But some sites can beat this time). A blog I created at the start of June was included about a week ago, but Yahoo does include these information sources faster.
If a site is already in the index, changes to the site and new pages can be included within one to two weeks.
My impression was that the listings were changing every one to two weeks, so that is quite good. Partic as I am creating new pages for an existing site.