So gonna a bit hunt regarding this issue & find out some statements!
Case 1: Google builds a new filter to check the websites in the Top 10 for major searchable keywords (Not any manual review).
If a website ranks for a major searchable keyword within short time! The filter triggers and push the website (which enter into TOP 10 within short span of time) to 2nd or 3rd page or even 5-7th pages (Even if the site optimized correctly). If it is done by Black Hat/Grey Hat, Google have no mercy to make it invisible for some weeks/days. Then place it above 20th pages(May be in Google omitted results).
Case 2: Google checks the Top 10 website's back-links age.
Google push the website back, when the back-links age is less than 60-90 days (SEO master's itself got confused with this range - Can't find what Google determined for back-links age?). So we may not expect the results sooner.
Do not trust the above sentences 100%, But this what I heard from black hat monsters. I don't thing the statements are completely "myth". If it is myth Can you guys tell me what Google webspam team thinks now? Understand the above words if you're struggling with SEO!