When referring to the sandbox phenomenon, does the period refer to how long ago the domain was purchased or when Google indexed it for the first time?
It generally refers to the period when a new site fails to rank for anything. Many believe Google holds a new site in the "sandbox" while it determines it's validity in attempt to prevent creation of spam sites. In SEOing 100's of sites i've never really experienced it myself, if you know what your doing you will rank right out of the starting gate.. and if you don't just blame it on the sandbox phenomena.