Yahoo, paid links and SERP result improvement

Hypothetically, lets assume I purchase a few links from sites considered to be authority by Yahoo.

When can I expect improved SERPs. Is it within a few days or do I have to wait for Yahoo to re-build the index. How often does Yahoo build its index.

I know they post some weather reports, but is there some site/link that tracks all approx dates this happened in the past?

Please advise.

 

You should see results in a few weeks.

 

and how often is the index built?

 

I don't know....Whenever I do anything significant SEO wise...I usually see results in 3 to 4 weeks...