What do you know about Google Sandbox?
 

Google Sandbox is a kind of observation by which you will be able to get necessary information about the way Google search engine ranks web pages in its index. Existence of this specific has not been confirmed yet, and so many debates are going on all over the world related to this topic. According to some believers, this tool is designed to filter different web links for improving the web page position. This filter is considered to check the active age of a domain and competitiveness of keywords. The presence of the Google Sandbox and its effects has been long debated as Google has not made any disclosure on this matter.

You are right at some extent because sometimes Google keep those websites in the SandBox that has been penalyzed or made some violations of its rules and after a review sometime it restores early or sometime it restores later.